Not reaching max RPM?

[Hunterb]

Hi all,
Before I start chasing my tail I thought I would ask a quick question here in hopes that I might get pointed in the right direction.
I have a 1997 GTX with a rebuilt (by me) motor that has run flawlessly for the last two years. I don't drive it a lot, it's mostly a kids toy, so I'm not sure when this started happening but for some reason it recently started not reaching the RPM's it used to. It's great up to about 6000 and then just won't climb any higher. I've lost at least 5mph from top speed. I haven't changed anything as far as carb settings or made any other changed and other settings. What would people suggest to look for as far as 'most likely to least likely' causes. It starts no problem and pulls hard up to about 6000 and then just seems to stop accelerating. No stumbling or missing, it just doesn't go as fast as it did last week.
Any suggestions would be appreciated.
Bruce

 

[GGuillot]

Hi all,
Before I start chasing my tail I thought I would ask a quick question here in hopes that I might get pointed in the right direction.
I have a 1997 GTX with a rebuilt (by me) motor that has run flawlessly for the last two years. I don't drive it a lot, it's mostly a kids toy, so I'm not sure when this started happening but for some reason it recently started not reaching the RPM's it used to. It's great up to about 6000 and then just won't climb any higher. I've lost at least 5mph from top speed. I haven't changed anything as far as carb settings or made any other changed and other settings. What would people suggest to look for as far as 'most likely to least likely' causes. It starts no problem and pulls hard up to about 6000 and then just seems to stop accelerating. No stumbling or missing, it just doesn't go as fast as it did last week.
Any suggestions would be appreciated.
Bruce

Difficult to say exactly what's causing it. Start cking stuff. It could be a drag with the drive line robbing power. If you haven't cked in a while I'd pull the jet pump and ck. Bearings going out, I had a similar drop in top speed and RPM just before the impeller shaft melted the thrust washer and bearing to it. Is anything wrapped around the driveshaft? usually that shows itself with a vibration, but not all the time.

You could ck the RAVES being dirty or not opening up, but that's usually noticeable up to 5000 rpm.

 

[etemplet]

I'd do a compression check just to be sure. You could go right to the water control valve and see if it is leaking. It is mounted on the water box and looks similar to a rave valve. It the bellows is leaking or the bottom clamp rusted you'll loose RPM on top. You could have rave valve issues as well. Good Luck.

 

[POPPS]

You also could have a fuel delivery issue, up stream or down stream,,,in the carbs.,,Etemplet has verygood suggestions to follow.

 

[Hunterb]

I'd do a compression check just to be sure. You could go right to the water control valve and see if it is leaking. It is mounted on the water box and looks similar to a rave valve. It the bellows is leaking or the bottom clamp rusted you'll loose RPM on top. You could have rave valve issues as well. Good Luck.

Ok. Thanks for that. I'll check the water control valve. I checked the raves and they seem to move easily and smoothly. Unfortunately I have very limited tools at the moment so I can't do a lot till my wife comes out tomorrow with my tool box.

 

[Hunterb]

My first thought is fuel d

You also could have a fuel delivery issue, up stream or down stream,,,in the carbs.,,Etemplet has verygood suggestions to follow.
[/QUOTE
My first thought was fuel delivery. Possibly a plugged filter in the carb or the strainer. It just feels like it runs great and then just isnt getting fuel for those last 500 or so rpm. I really dont feel like pulling the carbs so I'll check the other stuff first.

 

[etemplet]

Did you replace the spark plugs. Also clipping the end of the spark plug wire 1/4" if you have the length and you think you have a problem. I don't clip them unless they look bad. You can pull on the wires and if they pull out you need to get them secured. This is a common problem and when the spark breaks down performance suffers.

If you want to see if it is a fuel issued gently pull out the choke and see what happens. many of us have had our share of weird problems. Good Luck.

 

[Hunterb]

Did you replace the spark plugs. Also clipping the end of the spark plug wire 1/4" if you have the length and you think you have a problem. I don't clip them unless they look bad. You can pull on the wires and if they pull out you need to get them secured. This is a common problem and when the spark breaks down performance suffers.

If you want to see if it is a fuel issued gently pull out the choke and see what happens. many of us have had our share of weird problems. Good Luck.

I didn't change the plugs but I did pull them out. They look perfect, no fouling at all and a nice chocolate milk colour on the insulator. I have another set somewhere and will stick them in tomorrow.
Thanks for the reply.

 

[etemplet]

I tell ya... these two strokes can foul a plug real quick. Good luck man.

 

[Hunterb]

I tell ya... these two strokes can foul a plug real quick. Good luck man.

Etemplet wins the prize for best diagnosis. I took the cap off the water regulator and the spring came out in 2 pieces. I can't get a proper replacement here so I got the same diameter and strength spring from an auto shop and cut it to length, put it in and instantly had full rpm's again. I'll order the proper one when I have a chance but, for now, I'm back in business.
I'd buy you a beer but I'm way out on the west coast of Vancouver Island which I suspect is a ways from you.
Love this forum.

Bruce