Gas Gas JTR 370 won't run without choke on.

[_smf_]

I bought this bike from my friend for cheap. He had it sitting in his garage for a few years.

It seems to have good compression from what I can tell, I will check with tester soon.

I took carb off and cleaned out twice. I made sure to blow out all the passages and clean filter in carb body and checked petcock on tank. Everything seems to be flowing good. I also removed jets and blew them out and cleaned with carb cleaner. Powerwashed airbox out and also cleaned air filter. It has a dellorto carb. Any help is appreciated, thanks.

Stuart.

[b40rt]

did you re-oil the filter ?

[lineaway]

pilot circuit is plugged some where. And/ or the lower choke circuit, the pipe in the float bowl.

[_smf_]

did you re-oil the filter ?

No I didn't. I only took it for a quick spin around the driveway and had the same symptoms immediately so I don't think it ingested any more dirt. I guess I'll take it apart again and oil the filter this time. Thanks for the replies.

[_smf_]

pilot circuit is plugged some where. And/ or the lower choke circuit, the pipe in the float bowl.

That might be my problem. I didn't remove the pipe part to clean it. I just sprayed it with carb cleaner and compressed air. I'll disassemble that too tomorrow. Thanks.

[jse]

That might be my problem. I didn't remove the pipe part to clean it. I just sprayed it with carb cleaner and compressed air. I'll disassemble that too tomorrow. Thanks.

The 96' JTR370 uses the Dellorto PHBH26CS carb (also known as the "large body" oval bore Dellorto, also used on Fantics) and it is a little tricky at times (it was only ever used on this bike and only in 96'). You'll need to remove the jets and really check them for any obstructions, especially the pilot. Sometimes some very thin copper wire (a strand off some electrical wire) can be used to clean out any corrosion, which will not always come out with compressed air. Hold the jet up to the light to make sure the hole is round and clear. You need to blow air through the jets and passages in the carb in the opposite direction the fuel flows. The orifices are usually tapered like a funnel and blowing in the same direction as fuel flows will often just lodge the grit in the holes further.

Jon

A common conversion for the 370 was to use a PWK28 Keihin carb, do you know what kind you have on it?

Edited November 28, 2010 by JSE

[_smf_]

The 96' JTR370 uses the Dellorto PHBH26CS carb (also known as the "large body" oval bore Dellorto, also used on Fantics) and it is a little tricky at times (it was only ever used on this bike and only in 96'). You'll need to remove the jets and really check them for any obstructions, especially the pilot. Sometimes some very thin copper wire (a strand off some electrical wire) can be used to clean out any corrosion, which will not always come out with compressed air. Hold the jet up to the light to make sure the hole is round and clear. You need to blow air through the jets and passages in the carb in the opposite direction the fuel flows. The orifices are usually tapered like a funnel and blowing in the same direction as fuel flows will often just lodge the grit in the holes further.

Jon

A common conversion for the 370 was to use a PWK28 Keihin carb, do you know what kind you have on it?

It's the original dellorto carb on it now. I did clean out the pilot with a small piece of wire and checked it to the light. It seemed to be ok. I will try blowing the air the opposite way this time. Thanks.

[_smf_]

It's the original dellorto carb on it now. I did clean out the pilot with a small piece of wire and checked it to the light. It seemed to be ok. I will try blowing the air the opposite way this time. Thanks.

Ok, I cleaned it out again today. Seemed to be clean with no dirt. The pilot jet didn't look clogged either. I did notice the intake boot from the carb to the cylinder looked worn out. Could a vaccum leak there cause the symptoms I'm having?

Stuart.

[petwar]

if there is a split in amy part of the intake this will cause un-metered air to be sucked in making the mixture too lean. putting the choke on will cause the mixture to richen up. i would check all of the gaskets and rubbers for splits or leaks.

[_smf_]

if there is a split in amy part of the intake this will cause un-metered air to be sucked in making the mixture too lean. putting the choke on will cause the mixture to richen up. i would check all of the gaskets and rubbers for splits or leaks.

I did as you advised and checked out all the gaskets seals etc. I also pulled off the reed cage and the reeds seem to be worn out too. There is a visible gap where they are supposed to be sealing. Could that have something to do with my problem? Thanks for the info.

[jse]

I did as you advised and checked out all the gaskets seals etc. I also pulled off the reed cage and the reeds seem to be worn out too. There is a visible gap where they are supposed to be sealing. Could that have something to do with my problem? Thanks for the info.

If the reeds are frayed at all (usually on the outer edges) they should be replaced. If the ends bow up at the cage sealing surface, causing a gap of about .015" or more, they also should be replaced. Theoretically you could reverse them to get the ends to lie flat on the cage but the normal movement of the reeds usually causes a "stress riser" cut where the plate holds them on the cage and they would soon fail. Boyesen dual-stage reeds are a really good choice for the 370.

If the manifold has cracks in it I'd replace it. Some early thick 370 manifolds are prone to cracking and will just get worse (they also were used to adapt the Keihin PWK28 to other displacement engines as the PHBH spigot is about the same diameter of the Keihin spigot).

Jon

[_smf_]

If the reeds are frayed at all (usually on the outer edges) they should be replaced. If the ends bow up at the cage sealing surface, causing a gap of about .015" or more, they also should be replaced. Theoretically you could reverse them to get the ends to lie flat on the cage but the normal movement of the reeds usually causes a "stress riser" cut where the plate holds them on the cage and they would soon fail. Boyesen dual-stage reeds are a really good choice for the 370.

If the manifold has cracks in it I'd replace it. Some early thick 370 manifolds are prone to cracking and will just get worse (they also were used to adapt the Keihin PWK28 to other displacement engines as the PHBH spigot is about the same diameter of the Keihin spigot).

Jon

Thanks, I have been researching some of this stuff and I read that worn reeds will make an engine run richer so I don't think that is my main problem, although I will replace them anyways. I think I'm going to check out the float height and then the crank seals. Anyone know what the float height should be set at?

Stuart.

[jse]

Thanks, I have been researching some of this stuff and I read that worn reeds will make an engine run richer so I don't think that is my main problem, although I will replace them anyways. I think I'm going to check out the float height and then the crank seals. Anyone know what the float height should be set at?

Stuart.

The float arms should be level with the sealing surface on the carb body as I remember (carb held upright and then tilted 45 degrees)

DELLORTO PHBH26CS (26mm OVAL PORT) SPECS:

MAIN: 115

PILOT: 45

NEEDLE: X18 (3rd CLIP POSITION DOWN FROM TOP)

SLIDE: 55

AIR SCREW: 1.5 TURNS OUT TO START (NOTE: THIS IS AN AIR SCREW ON THIS MODEL)

Jon

[_smf_]

The float arms should be level with the sealing surface on the carb body as I remember (carb held upright and then tilted 45 degrees)

DELLORTO PHBH26CS (26mm OVAL PORT) SPECS:

MAIN: 115

PILOT: 45

NEEDLE: X18 (3rd CLIP POSITION DOWN FROM TOP)

SLIDE: 55

AIR SCREW: 1.5 TURNS OUT TO START (NOTE: THIS IS AN AIR SCREW ON THIS MODEL)

Jon

Thanks for the help it was the float level, runs good now. I just have to get the brakes and clutch working acceptably now.