Hi, I am new to the TY forums so if I break any protocol I am sorry and would appreciate any direction that would prevent me from doing it again. Anyway, a couple of months ago I bought a 1977 Yamaha GP 440 that was "freshly rebuilt" (you know how that goes) but it didn't have any compression on the one cylinder. I tore it down and replaced the pistons and rings and checked everything over and it seemed ok. I put it all back together and now a get a very random back fire when it's running. Can anyone give me any clues as to what I am up against here. A buddy of mine is a die hard John Deere sled fanatic and I can't be having problems with the Yami when we're out cruising around.
RON HYDRAULIC YAM
Member
chipper ... make sure both plugs are burning the same colour , hope you included crank seals in rebuild .
..it could be lean on one side from a crank seal ... never seen the reed valves stick,,, crank seal causes one side
to draw more fuel than other and can mis fire.
The mufflers on those fall apart and can block the tail pipe hole and mice make nests in them..
Mag side seal can let oil residue on your points (points set with TDC meter and not a "gap" setting but
they will tolerate some guess work)...
The oil injects into the manifold according to RPM and throttle setting... wide open / fast.. to long slow downs, pumps in
more oil than it needs as only idle amounts of gas are drawn in... tend to give you a blue cloud when you giver again but
seldom miss fire.
Try and keep track of the circumstance that causes it... check easy spots first ...muffler.
These are similar to my 77 PR440's.
Ron
..it could be lean on one side from a crank seal ... never seen the reed valves stick,,, crank seal causes one side
to draw more fuel than other and can mis fire.
The mufflers on those fall apart and can block the tail pipe hole and mice make nests in them..
Mag side seal can let oil residue on your points (points set with TDC meter and not a "gap" setting but
they will tolerate some guess work)...
The oil injects into the manifold according to RPM and throttle setting... wide open / fast.. to long slow downs, pumps in
more oil than it needs as only idle amounts of gas are drawn in... tend to give you a blue cloud when you giver again but
seldom miss fire.
Try and keep track of the circumstance that causes it... check easy spots first ...muffler.
These are similar to my 77 PR440's.
Ron
Unfortunately I didn't change the crank seals. But the plugs are both a nice tan/brown color and when I had it all apart I noticed the baffles in the muffler rattled around but I didn't think too much of it. I just took the muffler off and started it up for just a few seconds (maybe 30) and it never backfired. I'm leaning toward the muffler being the culprit because there isn't much consistency in when it backfires. I wonder what the odds are of finding a good muffler around?
Well I took all of the guts out of the muffler and it runs like a dream. No backfires and it scoots right along for a 440. Now I have a new problem, the throttle likes to stick every so often. If the kill switch didn't work I would have a new opening in my garage.
RON HYDRAULIC YAM
Member
That's nice ... They sound good with the guts out and still are not noisy... I rattled my innards to the tail pipe hole
and extracted with long nose pliers,, You are lucky if that tail section hasn't rusted out. I have a few of them.
I'm thinking there should be a clip at top holding conduit to kill switch and a clamp at the carb as well to keep the outer still.
Maybe add a "bit" of spring at carb as the throttle shaft , oil rod or squirt fuel linkage might be tight rather than cable..
Cable fits these other models as well ...you might want to where the tether cord ??? if it happens to be any good, most are not..
1974 GP292F GRIP - WIRING
1974 GP338F GRIP WIRING
1974 GP433F GRIP WIRING
1974 SL338F GRIP - WIREING
1974 SL433F GRIP WIRING
1974 SM292F GRIP - WIRING
1974 TL433F GRIP - WIRING
1976 GP300 GRIP WIRING
1976 GP440 GRIP - WIRING
1976 GS300 GRIP WIRING
1976 GS340 GRIP - WIRING
1976 PR440 GRIP - WIRING
1977 GP440A GRIP - WIRING
1977 GS340A GRIP - WIRING
good luck
Ron
and extracted with long nose pliers,, You are lucky if that tail section hasn't rusted out. I have a few of them.
I'm thinking there should be a clip at top holding conduit to kill switch and a clamp at the carb as well to keep the outer still.
Maybe add a "bit" of spring at carb as the throttle shaft , oil rod or squirt fuel linkage might be tight rather than cable..
Cable fits these other models as well ...you might want to where the tether cord ??? if it happens to be any good, most are not..
1974 GP292F GRIP - WIRING
1974 GP338F GRIP WIRING
1974 GP433F GRIP WIRING
1974 SL338F GRIP - WIREING
1974 SL433F GRIP WIRING
1974 SM292F GRIP - WIRING
1974 TL433F GRIP - WIRING
1976 GP300 GRIP WIRING
1976 GP440 GRIP - WIRING
1976 GS300 GRIP WIRING
1976 GS340 GRIP - WIRING
1976 PR440 GRIP - WIRING
1977 GP440A GRIP - WIRING
1977 GS340A GRIP - WIRING
good luck
Ron
Hey Ron, would you happen to know anyone out West looking to part with any PRs or EWs? I've been looking for quite some time but luck is thin on those beauties out west in Alberta
RON HYDRAULIC YAM
Member
Hi Jamesbob ... I have sent you a PM with 2 possibilities..... Rick Schrader ??? used to have a "brand new" never sold
at a dealership out west ... I'm not sure about name ,,, Was a 74 TL433F ....
Google each of the models ew643 tl433 tw433 pr440 and disregard my posts... and watch for sale ....
email me and I will add to contacts in case I see one.... email on PM
Ron
at a dealership out west ... I'm not sure about name ,,, Was a 74 TL433F ....
Google each of the models ew643 tl433 tw433 pr440 and disregard my posts... and watch for sale ....
email me and I will add to contacts in case I see one.... email on PM
Ron