A forum for owners of Yamaha TTR250 trail and enduro bikes!

tracker · Veteran Member

Engine surging

domski1 · Senior Member

Have you deffinetly checked the carb stub for leaks as the rubber comes away from the metal part and it is quite hard to spot on the bike? It does sound like a air leak!

TTRfan · Super Guru

domski1 wrote:
Have you deffinetly checked the carb stub for leaks as the rubber comes away from the metal part and it is quite hard to spot on the bike? It does sound like a air leak!

I agree Adam. I recollect a suggestion that this could be checked by spraying someing on the inlet stub whilst the engine is running but can't recall what it was - WD40 perhaps?

Brian

sammyttr · Senior Member

spray wd40 around the inlet if the revs increase you have a leak :D

barra8 · Guru

Best thing to use is Start-ya-bastard or carby cleaner,wd40..

As to the problem...It could be a number of things...

Pet**** valve filters blocked...Solution... Clean Pet**** valve filters

Float sticking (low or too much fuel) Solution...clean & check float level is about 3/4 full in the bowl & the float is shutting off level with the carby.

Jets blocked Solution... re-check jets are clean sideways aswell as through the centre.

Air passages blocked...Leave carby overnight in kero or similar & Blow out all holes with an air compressor.

Choke/start plunger seal perished....Replace seal

Bad Earth.....check main ground

...........................................................................

If i think of anymore possible solutions i will let you know .

.....................................................

Brian & others may want to check out this great stuff

.............

Jarrah.

-- Edited by barra8 on Wednesday 24th of October 2012 08:23:12 PM

tracker · Veteran Member

Thanks for the replies.I had sprayed maintenance spray around the inlet but didn't notice anything,I'll try again.Whether it proves it or not i will remove the inlet stub.I will let you know the results.

barra8 · Guru

There is one screw on the side of the carby...it bolts the fuel pump bracket/arm into the carby.

There is one screw that holds the slide arm down.

Four screws in the top.....holding the top on.

Two screws to hold the slider onto slide arm.

Other than that there is no other screws in the top that i can think of from the top of my head..

Not sure why any of these would cause the problem described but the one at the top of the carb that holds the fuel pump arm on as he mentioned that he had cleaned it already (assuming he tightened these?).

...........................

Jarrah.

-- Edited by barra8 on Thursday 25th of October 2012 07:43:47 PM

barra8 · Guru

I think it is more likely to be dirt in carby or it's not put back together properly.

.....................

When did it start to happen?

Does it happen constantly or just when you start it up when cold?

What do you mean by engine surging? Revs going up & down? or just dieing all together.

Is it blowing smoke?

Any other symptoms?

............

Jarrah.

-- Edited by barra8 on Friday 26th of October 2012 01:12:17 AM

TTRfan · Super Guru

I was talking to a mate who had a stalling problem on his TTR that was almost impossible to trace. Turned out that there was a loose screw inside the top of the carb. He tightened it up, peened it over and the problem was solved. Just wish I could recall exactly what had worked loose - sorry disbelief

Gotta be obvious though...........

Just a thought though if nothing else is obviously wrong.

Brian

tracker · Veteran Member

I sprayed the inlet with WD there was no change.I have now removed the inlet stub, but can see nothing obvious.Iwill have another look at the carb.Thanks for all the replies,please keep them coming,I'm sure we'll find the cause.

TTRfan · Super Guru

tracker wrote:
I sprayed the inlet with WD there was no change.I have now removed the inlet stub, but can see nothing obvious.Iwill have another look at the carb.Thanks for all the replies,please keep them coming,I'm sure we'll find the cause.

Sometimes with a problem like this, you need to do what we did with my mate with the stalling problem - swap carbs to either confirm or exclude the carb as the culprit.

Turned out to be his carb so he just had to go through his carb methodically until he found the fault - which was a loose screw.

Do you have another TTR owner living locally you can swap carbs with?

Brian

tracker · Veteran Member

The engine starts and idles ok,when i increase the revs it seems like it is running out of petrol.
I think this is happening when the main jet would come into play.

"Do you have another TTR owner living locally you can swap carbs with?"
No i haven't.

"or it's not put back together properly."
Unlikely the carb hasn't been touched for over three years.

Will strip the carb again
So far i have tried another exhaust,two different coils,different HT lead and cap.

barra8 · Guru

tracker wrote:
The engine starts and idles ok,when i increase the revs it seems like it is running out of petrol.
I think this is happening when the main jet would come into play.

"or it's not put back together properly."
Unlikely the carb hasn't been touched for over three years.

Will strip the carb again
So far i have tried another exhaust,two different coils,different HT lead and cap

If you took it apart there is always the chance that you got it wrong...nobody is perfect,we all make mistakes.

As to the problem your on your own if you cannot describe it well enough. I would have liked to have known what you mean by surging...

Firstly...

Does it splutter?..

Does it backfire?...

Does it have a flat spot & get past it?...

Or is it constantly there just as a noticieable flat spot (surging) without any other symptoms.????

Next...

Does it have good compression?

Checked spark plug against motor while cranking the motor over to see if it has nice bright blue spark constantly without fault?

What is the spark plug gap?

..........................

Jarrah.

-- Edited by barra8 on Sunday 28th of October 2012 05:54:22 AM

Haggis Hunter · Veteran Member

Have you checked the fuel tap to see if there is a good flow through it? Or the fuel line, is there a good flow through that?

Does it run better with the choke out?

Has the air filter been checked?

Had a problem on an engine some years ago with a mis-fire on one cylinder on a 6 cyl engine that had the head gasket replaced. Took the inlet manifold off and found a piece of rag jammed in the inlet tract of the missing cylinder.

Have also seen foam filters that are choked pulled into inlets.

Peter

-- Edited by Haggis Hunter on Sunday 28th of October 2012 11:23:08 AM

barra8 · Guru

barra8 wrote:

If you took it apart there is always the chance that you got it wrong...nobody is perfect,we all make mistakes.
As to the problem your on your own if you cannot describe it well enough. I would have liked to have known what you mean by surging...
Firstly...
Does it splutter?..
Does it backfire?...
Does it have a flat spot & get past it?...
Or is it constantly there just as a noticieable flat spot (surging) without any other symptoms.????
Next...
Does it have good compression?
Checked spark plug against motor while cranking the motor over to see if it has nice bright blue spark constantly without fault?
What is the spark plug gap?
Petc0ck valve filters blocked?
Checked fuel line?
Carby overflow lines?
Float sticking? (low or too much fuel) Solution...clean & check float level is about 3/4 (full roughly 10mm from top of carby bowl) in the bowl & the float is shutting off level with the carby.
Jets blocked Solution... re-check jets are clean sideways aswell as through the centre.
Air passages blocked...Leave carby overnight in kero or similar & Blow out all holes with an air compressor.
Choke/start plunger seal perished....Replace seal
Bad Earth.....check main ground
...........................................................................
If i think of anymore possible solutions i will let you know .
.....................................................
Brian & others may want to check out this great stuff
.............
Jarrah.

Looks like that still leaves quite a few questions un-answered.

-- Edited by barra8 on Tuesday 30th of October 2012 09:50:10 AM

barra8 · Guru

Alot of the time if it was carby related you would hear a popping (slight backfiring) when using your gears to slow down -that is not very noticeable but still there.

You could also try turning your fuel off to see if it helps. This will not always indicate too much fuel as there is other causes but if it goes better for a bit until the fuel runs out it could be sticking float. It could also be weak spark.Another possible cause for this symptom is air box clogged or filter (although you did mention you cleaned it).

The symptom you describe does not mean you are running out of fuel. This could mean too much fuel,weak spark,(low compression although not likely) not enough air or not enough fuel so simply saying that it seems like it's running out of fuel tells me nothing.

.....................

Jarrah.

-- Edited by barra8 on Monday 29th of October 2012 12:16:03 AM

tracker · Veteran Member

" If you took it apart there is always the chance that you got it wrong...nobody is perfect,we all make mistakes."

The bike as been fine i.e. no running problems.I have only taken the carb apart to solve this ongoing surging.
To explain, have you ever run out of petrol?Well that best describes it.
Today i have stripped the carb again,i still haven't found anything.Tomorrow i will take the choke assembly apart,once i have shaped a spanner to fit .
Thank you all for your support.

barra8 · Guru

There is one other thing to try & that's dropping the carby pin down one or two settings.

Note: To do this raise the clip on your needle 1 or 2 settings.

Other than that all likely problems are listed above.

Good luck.

..............

Jarrah