Suzuki LTF250 Quadrunner diagnosis please

[hunterchub]

Chasing problems.

ATV is acting choked. Smells of gas. Black spark plug.

Idles fine. Soon as I hit gas it wants to choke out.

What I have done:

1. New fuel pump

2. Rebuilt carb

3. New throttle cable

4. Emptied gas

5. Checked pit cock

6. fresh non ethanol fuel

7. New NGK spark plug

Did all this and still dogs out when I hit the throttle. Idles fine.

Its worse when it get warmed up. Wont do hills very well.

Finally check the compression.

Cold it was 80 psi

Warm it was 100 psi

Book says range between 146 and 199 psi

Limit says 114 psi

Range seemed high to me. But I am probably wrong.

The ATV has had a hard life on the farm. Never did a valve adjustment.

Always changed the oil.

Is it time for a rebuild? Any recommendations.

I would say the ATV is valued at $1000 when running.

Your thoughts? Thanks. Scott

[hunterchub]

Update:

Sorry I ment to give more data.

2002 Suzuki LTF250F Quadrunner 4X4

Help!

[Tim-ANC]

You been wrenching a lot. Definitely adjust the valves. If you have one sticking open a bit it will effect your compression. Do you have a pet cock with a vacuum line on it?

[CraptainChaos]

Hi. I have a similar problem with my 94 LT-4WD. Tried most things listed above, and next plan to take the head off and check the valves & rings. Also mine puffs black smoke when starting, which leads me to believe that I am getting oil in the bore when left for a while.

Not much help I know, but wanted to let you know that you are not alone :-)

Cheers.

C

[hunterchub]

Tim ANC.

I do have a vacuum line on my petcock. It is clear as all the vacuum lines are clear.

Thanks.

[dtbprc]

my issue was blocked petcock (slowed it down) and vapor lock as gas cap was blocked. it would run 30 seconds then quit running. cleaned both and runs fine now. did rebuild carb beforehand - final adjust was to make throttle needle go further out. move it one notch.

[Tim-ANC]

Excellent. I had a tank venting problem on an old LT230. Would run for a bit then just sputter. After a while start back up again. Rebuilt the carb, changed the pet cock and in general banged my head on it. Vent wasnt big enough on the tank cap. Good idea on the needle jet adjustment too. I still recommend a valve adjustment if its never been done.

[dtbprc]

yes- my kids lt160 needs valve adjust as it runs hot but runs well- gotta do it

[hunterchub]

Thanks. This very frustrating. Any advise on doing a valve adjustment

[Tim-ANC]

Oil will drip out the fwd cap, put a rag over the exhaust pipe. Since, I dont have a feeler gage that fits in there well, I cut a strip of aluminum out of a beer can. Beer can walls are .005 inch thick. I assume you have a manual for this.

[hunterchub]

Thanks Tim. Yes I have a manual (downloaded off internet). Pictures are kindof poor. I have considered getting a Clymer (if available) or another book that may be appropriate.

[Tim-ANC]

Clymer is the best in my opinion.

[CraptainChaos]

Hi Hunterchub.

Did you get to the bottom of this?

I thought I had a breaktrough last weekend - I was checking the vacuum and breather pipes to the carb, and noticed that the fuel pump vacuum pipe was a little loose at the carb end. So trimmed it back to improve the fit in case it was leaking. The quad started great after that, and ran better than it had for a long time.

However, I just used it and although it did start great (better / easier than it ever has) and ran well, after about 10 minutes of use it started losing power and back firing again :-|

It seems that I cured one of 2 problems, and when the engine gets warm the main problem comes back to haunt me!

I am wondering if I could have a sticky valve, which is either jamming open when the engine heats up.... the engine heating is a red herring, and I just have a sticky valve??

I will try to get hold of a compression tester and check when cold/warm, but can anyone please suggest any other possible causes of power loss when engine gets warm.

Thanks

C

[CraptainChaos]

Hi,

I think I just found out why my LT-4WDX was starting well and loosing power / faltering when it got warm....

It seems to have not been when the engine warmed up, but after a period of time! Let me explain;

Having checked the fuel pump and valve clearnces I decided to buy a service kit and give carb a complete ovelhaul. When I removed the fuel needle valve housing I discovered a wad of fine fibre type crud backed up against the mesh which covers the bottom end of the valve housing.

It seems that while this wasnt causing a complete block, it was restricting the fuel flow to the bowl. And when the engine was demanding more fuel there was enough surplus in the valve for a short while, but after 5-10 minutes of work the restiction in the fuel supply meant that the carb could not deliver enough fuel in the mixture for more than about 10 min hard use at a time..... but on tick over it would run and run!

Anyway, carb has now had a good clean and been treated to new jets..... and crud removed. Tomorrow the quad is going to get some serious use, so fingers crossed.

Hope this helps someone out there.

Cheers

J

[Tim-ANC]

Wow, good find. What do you think the source of the fiber crud was?

[CraptainChaos]

I looked at it under a microscope once it dried out.... and it seems that the 'wad' was a mixture of various small/fine hair-like fibers and a whole lot of dust.

I can only guess that as the carb had not been serviced since I got the ATV .... and probably not for a long time before (maybe never since new in '95), and that in a previous life the quad was a farm vehicle. That the fibers may have been a mixture of fine animal hair and hey / grass, and that the dust /fiber wad had gradually built up over a very long period of time.

Anyhow, I used it yesterday pulling a harrow for a couple of hours and it behaved very well - started well and had plenty of torque. So it seems that the carb service & most likely the removal of fuel restriction cured it.

Cheers

J

[Tim-ANC]

Interesting. Does sound plausible.