Motor Surging Under Load

[tumtumsback]

Hey all,

Let me start off by saying I've done a lot of research on this forum, and unfortunately, I'm making this thread because I couldn't find anyone describing symptoms similar to mine. If a thread like this already exists, I'm sorry -- please delete this and link me to that thread.

I bought an 02 Blaster the other night, for a good deal, knowing it needed a bit of work to get it up to par. The motor revs out FULLY when either the clutch is pulled in, or when it's sitting still in neutral. If I am in gear, and go to give it gas, I can get all the way from 1st, to 6th gear, but only on a flat road, and just burbling off the bottom.

My first thoughts were to check the reeds, but they're perfect -- not cracked at all. I will say though, they were pretty wet, which made me think one of two things: 1.) The main jet might be too big, but that doesn't make sense because the bike is bone stock and the kid who owned it before me never made one engine modification -- or 2.) The TORS might be goofing up, and intermittently cutting spark, so a bunch of unburnt fuel is building up.

Also, I'd like to note the air filter on this thing was brittle, dry, and cracking, and I wouldn't be the least bit surprised to find out that a piece of air filter got wedged up in the carburetor somewhere (possibly main jet) causing these issues. Another theory someone came up with is that since the air filter on there now is so disintegrated, that there's not enough airflow restriction, creating a lean condition, and what I'm experiencing is the main jet not being able to keep up with this extra load of air coming from the airbox.

I'd like to pull off the carb, and see if the main jet is clogged; I started to take if off last night, and got the carb cap unscrewed off, but there was this one thin black wire getting in my way, and also I didn't know the best way to disconnect the oil injection line going into the carburetor.

Any help would be greatly appreciated! I want to approach this methodically, and not get too far ahead of myself wasting time + money on a leakdown and/or compression tester, etc. But at the same time, I don't want to create engine damage in the process of troubleshooting.

Thanks,
Colin

 

[blasterbrian]

Sounds like an air leak, did you leak test?
In my opinion i think the motor should be
Leaks repaired if any in cases then get oem yamaha gaskets replace all top ends gaskets and that air filter with a new oiled one, yamabond the reed cage properly because thats prob another source of air leak then you will need to clean carb, set float and check your jetting, dont forget to look over that air boot for cracks aswell as the exhaust for holes, i know thats alot of work but when all is said and done leak test before starting it and maybe give it a heat cycle before riding and also a compression test
Just my 2cents

 

[blasterbrian]

Double check tors is removed
http://www.blasterforum.com/threads/how-to-remove-your-tors-88-02-models.655/
Make sure also if you have an oil block off the carb is blocked off too

 

[blasterbrian]

Also good idea to just bore and hone cylinder with new piston well your at it to make you bike last alot longer, check the whole bottem case well your at it for cracks, holes or anything not normal. Would recommend looking around the sprocket and bottem off engine

 

[blasterbrian]

Check your not running a junk china top end well you at it too, oem yamaha cylinder and wiseco piston,
Also if you do change top end you will have to run full heatcycles
Sorry for all the post just trying to help you find the problem lol

 

[tumtumsback]

Everything is 100% original on the quad. It's never been opened, nothing has ever been replaced. Super low hours. All original.

 

[blasterbrian]

Well id recommend getting that cast piston out and replacing it with a wiseco before it shatters
Also check piston skirt and cylinder for marks

 

[blasterbrian]

Doing it all right will guarantee you alot more time out of your bike dont kill it,
Blasters are an endangered species

 

[Larry's Shee]

First off take nothing else apart but the carb and exhaust. Now you can do a leak down test and compression test. Somewhere on here is a PDF repair manual. It will tell you how to remove the oil line and how to clean the carb.

A leak down tester and compression tester are the two mandatory testers for a Blaster. I use a Harbor freight leak tester and Craftsman is the least you want to get for a comp tester.
A rubber plug for exhaust and PVC cap for intake.

IF it passes the leak down test, clean the carb set the float try it again with a new air filter. Unplug TORS Brain box under hood, three wires Be sure to bleed the oil injection.
While exhaust is off inspect face and top of piston and what you can see of the cylinder wall. Also see if piston wiggles much.

If it ain't broke, don't fix it ! It already has stock Yamaha gaskets.

Actually was a recent thread with similar symptoms and it was missing the plastic slosh baffle on ! main jet. In the same thread I listed a bunch of things to do/check.

Keep us posted as to results and what you have done/checked.
Surging is a sign of lean fuel mixture.
Could even be plugged fuel cap vent or petcock filter.

 

[Larry's Shee]

FYI, there are a few on here that use only stock cast pistons.

 

[tumtumsback]

Fixed! TORS delete ftw

 

[Larry's Shee]

THANK YOU !! To often a problem is solved , but not shared with the rest of the class..

 

[tumtumsback]

The symptom matches the evidence too. The cylinder fins were wet with residue, seeping from where the reeds bolt to the cylinder. With TORS canceling out the spark, that unburnt fuel had to go somewhere!