New 1998 Mastiff... Already need help.

[roachdogg28]

First post here, but I just purchased a '98 mastiff for 1200$ with a supposedly bad starter solenoid and starter clutch. Turns out it was just one wire on the wrong prong on the run switch relay. Easy cheap fix there.

Then its running but only runs well above 4000 rpms with 1/2 to full throttle. If I try to let it idle, then it pops in the intake and dies.

So I rebuilt the carbs, adjusted float height, adjusted valve clearances (waayy to tight, negative clearance...) and verified cam timing.

So im thinking this bike has stock internals, but no airbox lid and very open slipon fmf muffler. It has a #48 pilot and on the third groove on both needles.

My next thought is maybe a bent valve. I will go get a compression tester and verify compression, but this leads me to the real problem of not having any specs for anything anywhere. Does anyone have any year mastiff manual? An also where do i get parts for this thing?

Photo attached to show what im working with.

[MZ in Oz]

Waste of time getting a compression test as auto valve lifter holds exhaust open until the bike fires up.
Adjust opening of secondary carb so it opens when primary is open 8-10 mm, 5/16 -3/8".
Idle mixture screw 3 to 5 turns out. Little diaphram on primary carb may be perforated,remove and hold over
small flashlight. Mine looked like a starry night but couldn't see any in normal light.

[roachdogg28]

Thanks for saving me the money on the comp tester.

I have tried the mixture screw at everywhere from 2-10 turns, doesn't change a thing.

Good tip on the air valve diaphragm. Haven't looked very closely at that. Will check it tomorrow.

Is there any precise way to verify combustion chamber is sealing well? The valve adjustment helped a lot, but didn't cure it.

Thanks for the help so far.

[roachdogg28]

I forgot to mention, if I increase exhaust back pressure, idle seems to clear up a bit. Definitely seems like a lean condition. I have high hopes for that diaphragm...

[DAVID THOMPSON]

check this for carb parts

http://www.siriusconinc.com/search_resu ... &x=24&y=16

[roachdogg28]

Thanks David, I expect I will be using that website quite a bit.

[roachdogg28]

So the diaphragm looks in great condition. no holes.

Anyone have any other ideas, things to check? This intake pop is not a big backfire, just a little poof i can hear then it dies. Seems to get worse as the engine warms and will only start on full choke.

So i started spraying carb cleaner everywhere to check for intake leaks, and sure enough the idle clean up and motor revs up a little when spraying near the top of the primary carb. Im not sure where in the hell i could be leaking from, but I think this is my problem.

[roachdogg28]

Found it.

This is why some ppl should just take it to the dealer. Prev owner missed putting this little guy back on.

[MZ in Oz]

That would be a problem. Hope it settles the running, a little more back pressure exhaust will help.
These motors don't really like an open pipe for running around the streets. Racing different matter.

[DAVID THOMPSON]

good one to check if it has set for a while rotten rubber tubing lurks every where