Genset Carb Problem

1) I use lacquer thinner, it doesn't evaporate off as quick.

2) Try blowing out passages with aerosol carb cleaner with the little red tube attached. (Watch your eyes) You will be able to see if there is a blockage.

3) I had a similar problem on my pressure washer and it turned out the choke plate had come free from the shaft and was sticking in the closed position.

4) No

Kramarat, TKU.

You have any comparative experience between lacquer thinner & commercial carb cleaners like Kleen-Flo?

I do use the aerosol cleaner after the bath. (A belt & braces philosophy.)

No mechanical issues, carb parts all move properly.

No, but I think they all work about the same. The commercial carb cleaners are typically just off the shelf solvents with a fancy name attached.

I also have a boat with a four stroke Yamaha motor on the back end, that wouldn't run right. I had gotten gas with water in it. I tore apart that carb about 6 times, at least. I finally realized that there were holes and ports in there that were damn near microscopic. I had to do a complete tear down, little tiny springs and stuff, if I remember correctly. I used the carb cleaner in a can with the plastic tube and ran it through each orifice and port in both directions, making sure they were completely clear. That finally got it running right.

I believe you are right though, it's got to be somewhere in that carb.

Have you tried disconnecting fuel line to carb and just letting gas from the tank run into an empty soda bottle and doing a visual inspection of the fuel itself? If you've got crappy gas/condensation in the tank it'll never run right.

kramarat, tku again. Today I pumped some fuel into a plastic glass & let it sit a while. No crap in the fuel & no sign of water/gas separation. On to the next thing...

I might suggest a stick type deodorant instead. Less harmful to the environment. Not to mention what Kleen-Flo must do to your underarms.

My first question is, Did you run it on an ethanol mix fuel? Why,because it will give you grief in small motors, especially if they are run infrequently. E10/15 fuel does not store well, and is not usable after 6 weeks as a motor fuel. Especially in small motors like gensets and mower et al. It will loosen and drag into the carb all the varnish and crud out of the fueltank and put it in the carb.

Acetone may lift some of the varnish in the carb, but you have to be sure there are no plastic/rubber parts.

CRC has a good aerosol carb cleaner, but you could also use the brake cleaner in a pinch.

Small carbs are way more fiddly to get right and you have to make sure that they have all the appropriate bits back in the right place. You also need to make sure that when cleaning out the various orifici that you don't damage them in the process. Like I said they're fiddly.

When you have finished, don't forget to clean out the fuel tank and replace the fuel filter. If there isn't one put one in the fuel line.

Tobugrynbak, TKU. Fuel source is the moho fuel tank. Ain't gonna clean that, it holds near $300 of gas. Much of our gas contains up to 5% ethanol, should not be an issue but I will double-check that. Still the cursed thing should start/run fine with a clean carb. Fuel fills the float bowl readily, so fuel pump & fuel filter are ok.

Many carb cleaners contain XYLENES (50-60%), METHYLENE CHLORIDE (40-50%), ETHYLBENZENE (5-15%) (Source: http://setonresourcecenter.com)so as far as the "best" carb cleaner, I would say that products available in most auto parts stores are going to be similar.

I am guessing that acetone would not hurt as long as all rubber and plastic parts are removed first.

As far as blowing out the carb with compressed air, I would not blow out an assembled carb but based on your comments, I am assuming that you do this after disassembly.

Your problem does not sound like a blockage. The fact that you're genny has black exhaust and the plugs are fouling so quick, indicates to me that too much fuel is being delivered rather than something being "blocked".

Have you checked to make sure the choke is fully opening after start-up?

Only other thing I can think of is a bad float valve assembly.

Good luck on this!

KJK/USA, tks...

I agree, way too much raw fuel... I dunno carb design, but I am guessing if there's a blockage in the "right" place, you get no atomizing air & all fuel. Float is set right & moves freely, it's plastic & has no leaks (I shake it at my ear & would hear sloshing if any leak into the donut), so it is not water(gas)-logged. I held the spring-loaded auto-choke fully open, no change.

If you can see the choke valve open, it would almost have to be float related. If you have a section of fuel hose that attaches to the carb, that is easily replaceable if damaged, try this. Use a small vice grip to restrict the fuel line. Slowly turn the adjusting screw on the vice grip and see if you can bring the gen set back to a normal mixture. If you go too fast, you will wind up shutting off all the fuel and the engine will stall. But if it starts to run good just before it stalls, you have found the problem. We do not know the specifics of your gen set, but some carb designs have a metering rod in the middle of the jet. That can back out and cause this problem you have. Good luck.

Bob C, tku 4 making me scratch my head.

The plastic float looks good & sounds good (no sloshing gas inside). It closes the valve when almost parallel to the carb casting/bowl line, just a hair low so as to be theoretically just a hair low of a properly full bowl. So I can't see any problem there.

This carb choke has a (passive) spring that pulls the butterfly open & a current-carrying spring that when cold, pulls the butterfly closed. When the current heats the spring, it stretches to allow the choke butterfly to open fully. When trouble-shooting, I removed the wires & controlled the choke manually, but was unable to find a sweet spot for the choke setting. (Holy hemlock, Batman... if I remember correctly the wire to the choke spring is always hot, ie, always carrying current... that would mean the auto-choke spring would always be hot & always have the same tension -- no automatic behaviour. Gotta double-check! TKU 4 giving my head a shake!)

Your thought on gradually pinching the fuel line is intriguing... is it applicable only to fixed jets? By cracking (towards closed) the adjustable needles on my run & idle jets, I can kill the engine, so I thought I was doing the same thing... yeah? Is there is a correct methodology for that? I've tried adjusting both needles in, but not at all systematic cuz I don't know a methodology. And I have lost patience on this problem, more than once!

On the metering rod question, for my idle needle, I didn't see any sign of any brass in the threaded aluminum casting. The run jet screws upward through the bottom of the float bowl up into the cast aluminum "stem" that is open to the centre of the carb barrel. The inside of the "stem" is threaded & contains a short orifice type of brass piece that is installed first, then a longer & larger brass piece that has maybe 8 sets of venturi holes, each set has maybe 4 holes around the circumference of the brass tube & the size of holes changes from one end to the other.

BTW, the genset is a 2-cylinder 1991 ONAN Model BDGxxx, & the carb I think is a "Nikki" (Japanese?)

I look forward to any further comment you have & I will check the points above.

Thanks!

Is this what your carb looks like?

Bob C, tku again...

No, my carb is different...

NIKKI, part # looks like...

Line 1: OZN
Line 2: 146 - 0443

I found a problem at/in the automatic choke. It has a wire heating element on a porcelain block inside the lean/rich adjustment 2-inch dia 'can' thing. A terminal is at each end of the element & the 2 leads connecting to these terminals both show battery voltage at all times. But the heating element is broken, no continuity across the 2 terminals. And if BOTH leads have battery voltage, how would the element ever heat up? Hah, gotta check with ONAN, something deeper might be out of order.

But I think it's an incidental problem, cuz I manually operated the choke & was unable to find any sweet spot for starting or running.

Check that some mudwasps haven't built a nest in the exhaust and partially blocked it.

This is NO joke.

Check also the intake silencer for debris/mud/gossamer/etc

Stu.

TKU Stu, interesting...

Not sure if we have any mudwasps or equivalent up here (Canada), & not sure how to check... muffler is fulla baffles of course, its outlet is maybe 2-3" long then it bends 90 degrees down & exhausts into air only 4" further along.

No silencer on intake air, but all is clean, with new filter.

Stu,

The real kicker for me on checking free-flow exhaust is simply that I hafta drop the genset out of the moho in order to remove the muffler. I hope that's not necessary, but if it is, you can bet I'll be looking at that as well as any other checks that require genset removal.

Tks

That ain't no 500 inch Cadillac you got there. If exhaust restriction is a concern still, just create some kind of leakage at the head surface. If you allow just a 1/8" gap around the exhaust manifold, it will be enough to make a difference, and you should see that if no load.

Hey Bob C, thank you for your further inputs...

Well, exhaust restriction is a concern just cuz I ain't found the problem yet. But honest, it is not easy to access! Still, you might have laughed me into giving it a try without dropping out the set.

You have an opinion on the impact of valve lash? The devil had been starting & running nicely all summer so valve lash was not an issue. But I gotta fess up when I prepped it for the moho last winter, valve lash was not on my pre-install checklist.

You have any thoughts on the possibility of an intake manifold leak? I had some backfiring on starter cranking, but I associated it with dicking around with the jets & it was almost 100% eliminated when the needles were near their proper settings. (It was not on my pre-install checklist, either.)

I still have some checking before I'm totally up against the wall. Ciao.

No need to drop the machine out of the moho.

Take out the spark plug, wind the motor over carefully 'till the exhaust valve is open, put your shopvac onto BLOW and place it over the exhaust pipe outlet.

Look for a meaningful volume of air coming out the plug hole.

I guess the shopvac on SUCK will get you airflow too, but it's too hard to quantify.

With the fact that it's just time from when you last ran it, it has to be from an influence like insects, animals or the like. You've eliminated varnish in the carb, and the timing gears are not likely to strip and alter with the motor stopped.

BTW check the timing, both valve and spark. Valve: valves 'rocking' equidistant to piston at TDC. Spark you already know about.

Don't know about this model ONAN but some motors have a split timing gear, spring loaded to quiet the gears and remove backlash. This could've fallen apart on the dying throes of the motor stopping last time. Left field tho'.

Cheers,

Stu.

Stu,

Interesting stuff you suggest. And challenging. (How much spark plug hole air would be 'meaningful'? All I know at this point is it will depend largely on airtightness of the connection to the exhaust.) To even reckon the ex valve open position is a challenge. I think I cannot even remove the flywheel shroud while in the cabinet.

So if I cannot make it happy on the latest iteration of carb cleanup & replacement of plug wires (to rule out intermittent spark), I'm inclined to drop the devil & do all/all mech checkout on the bench. Especially cuz I'd be on the learning curve as I tear apart this engine, and also cuz I'd be checking out more than exhaust constriction & spark & valve timing. (Electronic ignition, no timing mark, difficult in-situ to even measure rpm for tuning a new carb.) All points to bench testing for checking items beyond the readily accessible stuff.

I've done quite a number of Tecumseh carb cleanings (snowblowers) & occasionally I come across one that will not clean up. Now I guess I should have cut apart 2-3 of them to do post-mortems & figure out exactly why those blockages did not clear.

If this one doesn't clear, I will still not know if it's the carb or something else, so at that point I have 3 choices:

1, buy a new carb (but what if it's not a carb problem?); or

2, bench the puppy & tear down to check all other possibilities; or

3, before action, learn if the Onan tech can arrive at a bulletproof opinion on the carb without yanking the set.

TKU again. Will report asap if Genny comes glad soon, will report months later if I find the answer while it's on the bench. Wish me luck!

Ciao.

Take it 'as read' that the exhaust will be gas tight at the joints.

Check the airflow at the nozzle of the vac before you offer it up to the pipe. There will be some losses. Restriction, friction etc.

Gaffer tape the vac hose to the pipe and turn it on.

There HAS to be somewhere to put maybe even a screwdriver in to roll the Onan over with the plugs out. Remove the starter and lever the ring gear is another option.

With the blowing happening you'll soon discover when the valve is open, either cylinder, it doesn't matter. Any debris in the pipe will find it's way into the combustion chamber as an indicator. Vac it out.

IMHO the machine should not need tearing out of the moho.

It was working fine before the lay-up? The carb is now pristine. Only leaves the exhaust as a possibility.

Or a failed relay on the 12v excitation circuit. You'll have to get an Onan guy or a elec tech for that tho' I think. Curcuit is usually printed on the underside of the controll box cover. Check them. There is sometimes a relay controlled solenoid on the idle circuit of the carb. Shuts off any possibility of gas bleeding into the engine when stopped. Probably moreso on California models. Emissions and all that.

Does the controll panel have a frequency meter (Hz)? Most do. If the gen is a 4poler you'll get correct freq. at 1800rpm. (60Hz). 2poler you'll have to run to 3600rpm.

Point being is that you do have motor speed references available to you without needing a tach.

I could figure it if I was there, but, alas.................

Cheers,

Stu.

I'm with you, Stu. I don't think he needs to pull the gen.

Now, if it was me, I would take the fuel line off the engine and block it. Then the engine will be forced to run on only the fuel in the carb. At some point before the engine runs out of fuel, it will be lowering the fuel level in the carb bowl. The engine should lean itself out, and run well, at least for a few seconds. I have gone so far as to remove the carb, and rust squirt some gasoline into the intake manifold.

Here is another thing I have done as a repair on an engine that I suspected of having air passages clogged in the carb.

Run the engine up to about 2,500 to 3,500 rpm, and slam your hand over the air inlet, to shut off all air to the engine. Make sure the throttle remains open during this procedure. Allow engine speed to drop to 1,000 to 1,500 rpm, and then remove the air restriction. Do this over and over a few times. If the engine vacuum is applied to everything below your hand, it may suck any loose fitted junk in air bleed holes. And besides, the cost of this test is cheap. Good luck.

Bob,

That's exactly the ploy I use too.

Interesting note:

When I get a cantankerous engine that the choke isn't working properly on I usually start the engine by offering my propane gas torch up to the opening to the air cleaner. Or directly into the carb on some

Turn on the valve and the engine starts on gas( propane to you) easily. The torch would only ignite in the case of backfire, so immediately shut off the valve and flame stops. I need to say here that I've never had that happen in the 40 odd years of practicing the proceedure.

I use the proceedure often when starting up machinery which has lain idle for a while and the carb may be dry. I don't like killing starter motors winding up fuel with mechanical fuel pumps. The transition to a carb full of petrol (gas to you) is always seamless.

Cheers,

Stu.

I have never tried that in all the years. I do have a 3/4Hp 115 volt motor and an 18 volt cordless drill that I will use to spin over the small engines that are hard to start. Thanks.

You had 110 compression, forget about valve lash. If either valve was too tight, you would leak all the compression out the open valve. If the lash was a little loose, it would run, but have noisy lifters. Any other thing would have to be a mechanical failure, and having the same problem happen on both cylinders at the same time is VERY remote.

I still have not gotten an idea of what your gen set looks like. Is it overhead valves, or a flathead design? Opposed cylinders, or V design? Paper or plastic?

Brian,

Check to see that your float chamber gasket is not damaged.

Although probably not related to your problem,the flathead onans tend to need periodic removal of the carbon that accumulates under the heads. This carbon raises compression and causes problems.

Tks, Un... all's good in the float chamber.

I have cleaned the carb again with meticulous attention to verifying there is airflow in every passage that I can find.

I have found a problem with the auto choke in that both leads to its heater element are showing battery voltage. At all times. Of course that means the element is not heating, but there's no telling what other malfunctions lie behind that. (One thing for sure, the coach batteries die within 2 days).

So I will check what else has power 24/7, and eyeball the control box birdsnest of wiring & if nothing obvious, I install the carb & take the rig to Da Onan Hospital for electrical operations (MRI, cat-scan & a prostate exam).

My sincerest thanks to everyone. This site is a phenomenally good resource & not only have I much appreciated every contribution, I have learned useful stuff from many of them.

I will post the findings when all is good again.

if it has a fuel pump check the psi coming off the regulator. The needle and seat could be warn. Take the float bowl off and push the float up with your finger,this will stop the flow,if not you have a bad needle and seat,or a bad meetering rod and jet. I hope you tried running it with out the air filter.Did you check the valve lash. Was the carb a makuni , walbro,kiein or a holley 750 double pumper on top of a 671.

darren2264, tku.

Yep, done all of the above except the valve lash cuz I don' wanna yank the set out until it's last resort stuff. The carb is NIKKI. No regulator on fuel pump, free flow spurts good volume but only about 10" above the pump... spec calls for 3-5 psi, so gonna get a little more precise & ballpark SOH with 10 ft of vertical plastic tubing, poor man's precision pressure measure.

Drain all fuel from tank, fuel lines and carburetor. replace with fresh.

Replace air filter cartridge and fuel filter with new.

Remove muffler and confirm free air throughflow.

Check if engine is running with a partial choke, check choke lever if left on and if there is some other obstruction to airflow.

Resist using agressive cleaners in the carb, they make the clog worse. If air passages are lready clogged then you may have to replace the carb.

On most carbs there are small "welch plugs" that can be removed to clean the passages and jets underneath, however make sure you have the replacement discs from the manufacturer first, usually supplied in a carb overhaul kit.

If idle mixture adjustment jets have no effect then there is a blocked passage, or the engine idle rpm is set too fast while adjustment is being made.

One sparkplug may not be firing or there may be a loose contact or wire that is only allowing intermittent spark when running. Some twin cylinders have diodes between the 2 spark magneto ignitions which could be opn circuit or short circuit.

If the machine ran well when last used, and no-one has tampered or changed any adjustments, then it can only be dirt/blockage related.

Good Luck

Well, I read the comments. First, you've got a RICH mixture problem, which is too much gas for the air, which can be too little air or too much gas. The soot is unburned gasoline. There are places in a Nikkei carburetor (we need the model #) where a clog can cause too rich a mixture, specifically the emulsion tube, which mixes air with gasoline in the throttle mid-range. A clog in the air feed for the idle circuit shouldn't give you the soot, presuming you're operating the motor under load. You seem to be taking things apart a lot. Did you leave out or swap a washer? The internet has exploded carb diagrams with part numbers. We just troubleshot a 1981 Yamaha V-twin with almost identical carbs that someone had swapped parts inadvertently.

The float needle tip should be a perfect cone, no ridges. Check very carefully that there isn't an invisible piece of straw or grass on the float seat, and check the fuel pump pressure, although overpressure is a little unusual.

try this place: http://www.smokstak.com/forum/forumdisplay.php?f=1 or searspartsdirect.com read this thread http://www.smokstak.com/forum/showthread.php?t=79699&highlight=onan+BDG+Nikkei

Is this the carb? http://cgi.ebay.com/NIKKI-CARBURETOR-FITS-ONAN-B48G-P220G-some-B48M-NOS-/140468825642?pt=LH_DefaultDomain_0&hash=item20b4982e2a#ht_2971wt_522

Check the automatic choke

The emulsion tubes are probably blocked. They are very small and and even hard know if you have them clear once you have cleaned them. Air passes through them not gas. a carburetor that size has emulsion tubes probaly only one or two thousanths of an inch in diameter. Oxidation and deposits from dried fuel will clog them. You may want to strip a piece if copper wire and use one of the strands to clean out the tubes.

TKU... they sure don't appear to be constricted & I did poke a fine wire through all 24 of the li'l holes, but I have removed the carb yet again, so this time I will be sure to also use the carb cleaner on these.

Not sure if this applies here, but some carbs can fool you because when designed they control the amount of air to the mixture and when you think you are leaning out the fuel you are actually leaning out the air and that causes an overich mixture. Sometimes you have to think outside the box.

What make is the engine, may have a service manual to assist with your suspected carb problem?

h

Tks 4 your comments.

No problem with lean/rich, this carb follows the norm. The unit is Onan 1991, Model BGDxxx. I have the factory manual, it's no help in this situation (except I see the original carb had some extra parts in the bowl, related to the altitude adjustment, I believe... but no big deal cuz this puppy had run just fine all summer until the 5-week layoff.)

You say your float is ok, but check it by immersing it in hot water, and look for bubbles.

Also, do you know that the needle valve attached to the float is actually shutting off the fuel flow? Try inverting the carb and blowing into the fuel line port.The weight of the float should stop the air flow.If not, you have a dirty or worn seat or needle.

Hi,

If you shake the float close to your ear, if it's leaky, you will hear the gas sloshing around inside. But I liked your hot water immersion tip, so I tried it. No bubbles, float is good. And I also liked your valuable tip on checking the needle/seat seal. Much better than trying to replicate buoyancy lift with your finger. (The needle/seat seal also is good.)

Have a good day. For me, the carb battle continues... good thing I'm retired!

Hey fixx,

I was just checking in to see if you had run down the problem.

This may not apply, but I'll throw it out there. Most of these machines have a low oil cutoff switch. Is it possible that this switch is malfunctioning, or possibly wires shorting out somewhere causing the rough running?

kramarat, tku,

low oil pressure was the first thing I had checked.

see my last post (reply to "Redundant") for my current state of affairs.