white and black smoke with a little backfire

[kylem1184]

So my 85 350x has always backfired on when coasting down a hill in gear. But quick pops not big ones. But now when I start it I get a big puff of white smoke then it goes away when warm. Then once warm it will puff black smoke when I rev it quick. And now it will just die randomly I haven't done work on the top end so no risk of me screwing stuff up. Any help would be really appreciated the only thing I changed was I went from 89 ethanol gas to 92 ethenol free fuel. I have heard ethenol is hard on the classics valves.

[ATC-Eric]

The white smoke when it first starts, but goes away is going to be your valve seals. When worn out they will leak until it gets warm, and they make a better seal after it gets to temperature.

The black smoke is fuel a rich condition.

[kylem1184]

How do i keep it from dieing? It will literally run fine then I will give it gas and let off and it will die

[El Camexican]

Check your compression and valve clearance before you do anything else. Unless you live at an elevation higher than 4,000' the next thing to do is make sure your carb is clean and has the stock jets sizes in it and that the needle clip is in the center slot. The popping on deceleration is usually a sign of a lean idle circuit, a leak in the exhaust system, or head gasket. There should be a screw on the engine side of the carb that controls fuel at low speed or idle. Find out what the stock setting (turns out from closed) and set it to that. If it still pops open the screw (more fuel) 1/2 turn and try again. When the popping stops turn it back in (or out) a 1/4 turn at a time to see if its better or worse.

If you end up 2 turns out more than what the manual suggest as a starting point you need to change your pilot (AKA slow jet) to a larger one, but make sure the one you have in it now is clean before you do that. Adjust one size at a time.

This may help your stalling issues, but you may have other issues. Black smoke means rich, the opposite of the popping. Stalling can be cam timing, ignition, valve clearance, or low compression.

Good luck

[barnett468]

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yeah bummer.

here's some additional things to look at.

BLACK SMOKE

When you changed from ethanol which im guessing was E10 . . You actually made the bike richer . . I would first do the test below and if all is correct, i would go down 2 sizes on the main . . the spark plug chart should also give you some idea of what is going on.

i would start by doing the following:

If the gas is old or yellow at all, change it . . Yellow gas is either oil or contaminated by rust in the tank or both.

If the gas is old it can cause running probs . . if there is rust in the tank, iy can contaminate the gas.


Check the float level . . If it is excessively high, it can cause a rich or flooding condition.

..................Here's an example of it a little too high . . It should be just below the solid black line in your case . . If it is at the dotted line, it will still not cause a problem even though it is just a little high . . If if is above the dotted line, I would definitely fix it by bending the small metal tab slightly that depresses the needle, slightly upward toward the top of the carb.

If the float is plastic, it requires heat to bend it, and this should only be done by someone whom is very experienced, otherwise you might end up with a puddle of melted plastic which will no longer fit very well.

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............................................. Here's another in which you can see the is level way too low.


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Jetting can be determined to some degree by reading the spark plug . . it is best to have a new or very clean plug.

If it stutters/burbles even the tiniest bit when you accelerate, it is rich somewhere . . If it simply hesitates as if it is out of gas, it is lean.

You can post a photo of the plug . . The plug on the right is shiny which means it is wet which means its oily . . It is possibly rich too but its hard to tell because of black deposits from the oil . . This engine should be repaired . . The middle plug is good . . The left plug is lean.

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This plug is bone dry so the black means it is rich . . If both the threads and the porcelain is black, i would start by reducing the main jet size first . . In the case of a plug that has extremely heavy deposits like this, I would go down 3 sizes on the main because just one will not be nearly enough and two will likely no be enough . . Four would be too much.





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[El Camexican]

Barrnett (or anyone else) do you know of a commercial available drain plug with a fitting that can be temporarily used on a PJ or other Keihin that allows for a float level test like shown above? Or is there another way I can't think of.

[barnett468]

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Barrnett (or anyone else) do you know of a commercial available drain plug with a fitting that can be temporarily used on a PJ or other Keihin that allows for a float level test like shown above? Or is there another way I can't think of.

Hello Nico, A few people asked me that before and I unfortunately I don’t . . The simplest solution I have is to get another drain plug then get a 1/16” npt to 1/8” or 3/16” hose fitting or hose nipple . . The call them one or the other . . Then just drill and tap the drain plug . . Start by turning the tap only 3 times then test fit the fitting . . If you run the tap in too deep, the fitting will go in too far and bottom out which will guarantee a leak . . It is 92.375% guaranteed to leak anyway so plan on sealing it with Loc Tite or JB QUICK or that gooey brown Aviation Sealer etc.

These fittings come in steel, brass and plastic, and “should” be around $1.50 [25.4 pesos] at the hardware or auto store . . Some places like Aeromotive and Russel Performance also sell them but they attach fancy names and fancy applications to them or chrome plate them so they can charge $12.95 for them.

You can get them either straight or with a 90 degree.

As you know, you can obviously tape the top of the hose to your carb or something so you have another free hand if you need it.

Also as you know, after the test you can just turn your gas off and lower the hose to drain it etc to minimize the mess.

To drain the existing gas, I just hold a paint can can lid under the plug while I remove it if there’s room . . Sometimes I have to shorten them on a lathe or bridgeport mill.

If you can’t find any there in “Southern California”, you can try Amazon, Summit Racing, Ebay, Grainger, or McMaster Carr etc online.

https://www.google.com/search?q=1%2F...utf-8&oe=utf-8

[El Camexican]

I was hoping there was a commerciality available piece, but such is life. I'm going to make one. Thanks!

[barnett468]

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I was hoping there was a commerciality available piece, but such is life. I'm going to make one. Thanks!

yeah, ive never seen one and kawi didn't have any fancy things like that either . . none of the mx or road race works guys had anything for that either.

one could put miniature 1/16" fuel valve fitting in the drain plug and just leave it there if they liked to check the level frequently.

maybe i should make some and call them some fancy name and sell them for $19.95 . . the brass even has the "vintage" look.

[El Camexican]

LOL! Yea that would look great on a modern dirt bike.

I suspect I'll be doing my checking on a bench. Maybe I can make an adjustable holder to mimic the mounting angles of water the carb is off. I see some of the new Keihin's are measured at angles and not height.

Oops! Thread jacking. Yea kylem, check your float height on that Honda like Barnett said when you have it apart to clean.

[barnett468]

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Oops! Thread jacking. Yea kylem, check your float height on that Honda like Barnett said...

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