Author Topic: Fuel coming out of the air filter and dieseling engine. (Read 1377 times)

Protoolsuser81 · « **on:** January 03, 2014, 02:48:08 pm »

Well I had the quad start dieseling today and also there is fuel dripping out of the k@n. Not just a little but quite a bit and it has me concerned that something is wrong with the carb. Any idea's?

About the dieseling, I have read that dieseling usually comes from a leak and i'm wondering if the exhaust manifold leak can cause this? I'm going to use some rtv sealant on both the reed intake and the exhaust manifold. Is there a easy way a noob like me can do a leak down test pretty easy after that? I read something about the power valve being a issue with the lt250r but I don't know if there is any truth to this. Sorry for all the questions but I'm just trying to plan my next move with this quad.

Chuckie25 · « **Reply #1 on:** January 03, 2014, 02:58:44 pm »

It'll be your reeds

Protoolsuser81 · « **Reply #2 on:** January 03, 2014, 03:23:53 pm »

Well I guess it's time to buy some reeds then.

Do you know where I could get a new rubber boot that goes from my carb to the intake? I will attach a picture cause I don't think it's the stock one.

The carb has a indent where the boot has a lip and they fit together and the same with the intake but the rubber boot I have is missing some of that rubber lip and it's falling apart so I don't think it's sealing as good as it could. I would love to get a new one but i'm not sure where to get them. Any idea's?

LT250RWV · « **Reply #3 on:** January 03, 2014, 03:33:46 pm »

Boyesen rad valve is what you have. Check it before you buy reeds. Mine use to do it when I had it jetted to rich. Say I was half throttle from wide open mine would load up and split the gas back into airbox. Sound like you have a air leak or to lean pilotjet.

MotorGeek - Jerry Hall · « **Reply #4 on:** January 03, 2014, 03:41:27 pm »

It looks like you have a Boysen Rad Valve. If that is what you have you will need to contact Boysen to get the rubber boot.

Protoolsuser81 · « **Reply #5 on:** January 03, 2014, 03:42:20 pm »

I did just change the pilot jet to a 25 today. Also moved the main back up to a 280 to be safe. This can cause it to diesel like that?

Protoolsuser81 · « **Reply #6 on:** January 03, 2014, 03:44:22 pm »

Thanks guys, I will be contacting Boyesen to see about that boot. How do you tell if your reeds are good or bad?

Protoolsuser81 · « **Reply #7 on:** January 03, 2014, 04:08:43 pm »

I also just read about having the head shaved and getting higher compression and not having the right octane could cause dieseling as well. I just had my head shaved down and i'm only running 87 octane so now I'm wondering if this could be a issue.

Let me ask you guys this…..At what compression should you run what octane fuel?

LT250RWV · « **Reply #8 on:** January 03, 2014, 04:35:50 pm »

If you changed the pilot to a 25 thats is your problem im running a 40 pilot right now 15 degree weather. Only time I run a 25 is on my ported setup on stock carb that is in the dead of summer. If you dont quit messing with all your jetting circuits your going to fry that motor in the cold where you live one circuits at a time get it idling to 1/4 throttle adjust the needle to 1/2 . Then recheck to see if you idle is fine. Then go on from their 3/4 to wot throttle one at a time you need to read in tech section Carls write up about jetting l. I will bumb so you can read it. It will help if you choice to use it.

Protoolsuser81 · « **Reply #9 on:** January 03, 2014, 05:10:57 pm »

Well when I tested the air screw from bottomed out, the more I turned it out the higher the idol would go. I thought this was a indicator that the pilot jet was to rich?

LT250RWV · « **Reply #10 on:** January 03, 2014, 06:58:07 pm »

Go through the jetting steps I bumped, it will help you. Also, what mods are done to the quad?

BadMoonRacing500 · « **Reply #11 on:** January 03, 2014, 09:02:53 pm »

Quote from: Protoolsuser81 on January 03, 2014, 04:08:43 pm

i'm only running 87 octane so now I'm wondering if this could be a issue.
Let me ask you guys this…..At what compression should you run what octane fuel?

Never run 87 in a QR engine.... Minimum 92 on a mild 250. It is a QUADRACER and new gas is ethanol junk.

El Diablo · « **Reply #12 on:** January 04, 2014, 01:26:49 am »

If you can, run 100 octane Av or race gas.

Protoolsuser81 · « **Reply #13 on:** January 04, 2014, 07:31:09 am »

Where would I buy 100 octane? I think I'm going to go get a couple gallons of 110 and then mix it with the 87 I have now would this be fine?

MotorGeek - Jerry Hall · « **Reply #14 on:** January 04, 2014, 07:39:20 am »

Quote from: Protoolsuser81 on January 03, 2014, 04:08:43 pm

I also just read about having the head shaved and getting higher compression and not having the right octane could cause dieseling as well. I just had my head shaved down and i'm only running 87 octane so now I'm wondering if this could be a issue.

Let me ask you guys this…..At what compression should you run what octane fuel?

How much was shaved off of the head? How does the shape of the squish band compare to the shape of the top of the piston? What is the piston to head clearance? You may have shot yourself in the foot by having the head shaved. High octane fuel sometimes will not help some head shapes!

Protoolsuser81 · « **Reply #15 on:** January 04, 2014, 08:00:08 am »

I think he said like .15. I had a very good local motorcycle shop do this (they've been doing this stuff for as long as I can remember) and the guy told me just watch the compression because it was shaved down a bit. The head looks pretty simular to the way it was just cleaned up.

Dezsled · « **Reply #16 on:** January 04, 2014, 09:07:47 am »

The crown of the piston in comparison to the shape of the cylinder head combustion chamber is what determines the performance your machine will generate.

On a stock lt500 the shape isn't optimum, so the machine shops that are knowledgeable modify the cylinder head. Multiple builders here are up to speed on what's needed to turn your motor (250 or 500) into a dependable fire breather.

LT250RWV · « **Reply #17 on:** January 04, 2014, 11:41:03 am »

Was it idling with no run off before you changed your jets. You have the head shaved boyesen rad valve. What pipe are you running and is your quad porting.

PCS · « **Reply #18 on:** January 04, 2014, 12:45:07 pm »

Ask your motorcycle so where you can find hi octane fuel. Av gas can be found at an air port.

Protoolsuser81 · « **Reply #19 on:** January 04, 2014, 06:25:20 pm »

Ok so here is the rundown of what I did today.

I put in a 37.5 pilot jet and then got some 110 octane and did a 50/50 mix with the 87 octane. I ran it a bit and still had gas coming out of the air cleaner. The guy at another local motorcycle shop said my float must be sticking. I made sure everything was moving when I put the bowl back on and shook it around but still had the same problem. I also sprayed starting fluid all over the seals and had no idol difference.

What gives? Should I get reeds first or a new carb?

What kind of carb should I get if needed?

I also noticed the exhaust valve rod fell off in that little window and put that back on but really has no movement when I rev it. Still leaking gas out of the carb as well. Any advice here?

Also I still have to have the idol screw all the way in for a idol with 2 turns out on the air screw, and as I back the air screw out my idol still goes up and up. Does this mean my pilot jet is still to lean at 37.5?

Dezsled · « **Reply #20 on:** January 04, 2014, 06:52:59 pm »

When you checked the floats, did you remove them from the carb completely? The reason I ask is the float valve stopper has a rubber tip that over time becomes grooved sitting against the seat letting fuel leak past. After as many years it's been around it probably needs to be replaced.

A new needle wouldn't be a bad idea also, as they do wear down. Chasing problems it's best to start with parts that will give consistent/reliable results.

Protoolsuser81 · « **Reply #21 on:** January 04, 2014, 07:38:56 pm »

Quote from: Dezsled on January 04, 2014, 06:52:59 pm

When you checked the floats, did you remove them from the carb completely? The reason I ask is the float valve stopper has a rubber tip that over time becomes grooved sitting against the seat letting fuel leak past. After as many years it's been around it probably needs to be replaced.

A new needle wouldn't be a bad idea also, as they do wear down. Chasing problems it's best to start with parts that will give consistent/reliable results.

No I didn't remove the floats completely. Is there a way to fix this problem without replacing them?

I did however do a carb rebuild and put in a new needle and stuff like that.

Protoolsuser81 · « **Reply #22 on:** January 04, 2014, 07:40:18 pm »

Also how exactly do you adjust the floats on these stock carbs?

Dezsled · « **Reply #23 on:** January 04, 2014, 08:02:42 pm »

With the description of your leak check your float valve stopper.

I tried to find a vid but none of a mikuni flatslide for float valve adjustment. The keihin carb shown is very similar in function.

Protoolsuser81 · « **Reply #24 on:** January 05, 2014, 07:19:31 am »

Thanks for posting this Dez, this video was a huge help. I'm going to give this a shot today.

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Author Topic: Fuel coming out of the air filter and dieseling engine. (Read 1377 times)

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