Boats backfiring through carb

[Zhulkk]

I boat the boat a year ago and we had a bad lobe on the camshaft, so we got a new cam in and took it out it ran but had no power to plane.... We looked at the distributor and it was corroded so we replaced that and cleaned the carb and now it won't run and backfires out the carb... It's a 1992 cheetah with a 3.0 mercruiser

 

[glenn property of pam]

when you replaced the dizzy did you set the timing. Also did you make sure that number one cylinder was on the compression stroke and not the exhaust stroke (timing out 180 degrees).

 

[Zhulkk]

Yeah we timed, but if it was 180 degrees off would it still run?

 

[alldodge]

Yeah we timed, but if it was 180 degrees off would it still run?

If it is 180 out it will not run, and will be backfiring

 

[Zhulkk]

The thing is after we changed cams it was running it just had no power, so then we changed the distributor and cleaned the carb and now it's backfiring

 

[alldodge]

The thing is after we changed cams it was running it just had no power, so then we changed the distributor and cleaned the carb and now it's backfiring

Backfiring means the distributer is sending spark to the plugs before the intake valve is totally closed. Check your firing order on the distributer 1-8-4-3-6-5-7-2, make sure wires are in the correct order. If firing order is good, check timing

 

[Villain lll]

If timing is correct, you probably have a burnt intake valve or two. That will allow gases back up the intake side when plug ignites. It would also explain the lack of power you describe.

 

[nola mike]

Backfiring means the distributer is sending spark to the plugs before the intake valve is totally closed. Check your firing order on the distributer 1-8-4-3-6-5-7-2, make sure wires are in the correct order. If firing order is good, check timing

What he said, except you don't have that many cylinders

 

[alldodge]

What he said, except you don't have that many cylinders

:facepalm: dang I did it again, just got to quit drinking beer, nope that aint gona happen. Sorry it should be 1-3-4-2

 

[Zhulkk]

sorry i put it away for winter but am looking into taking it out pretty soon now that it is warming up, thanks guys!

 

[Zhulkk]

could it also be that the camshaft is off a bit?

 

[flipbro]

Did you break the new cam in properly? It only takes minites upon fire up to round a lobe if proper steps are not followed?

 

[Scott Danforth]

I boat the boat a year ago and we had a bad lobe on the camshaft, so we got a new cam in and took it out it ran but had no power to plane.... We looked at the distributor and it was corroded so we replaced that and cleaned the carb and now it won't run and backfires out the carb... It's a 1992 cheetah with a 3.0 mercruiser

your cam is most likely out of time

 

[Bondo]

The thing is after we changed cams it was running it just had no power, so then we changed the distributor and cleaned the carb and now it's backfiring

Ayuh,.... Sounds like it ain't gettin' gas,... How did ya clean the carb,..?? Complete tear-down,..??

Is the tank feedin' the fuel pump,..??
Is the fuel pump feedin' the carb,..??

Ya gotta start with the basic tune up,... throw in a compression test for good measure,...
That'll also answer Scott's question on cam timin',....

 

[Zhulkk]

Okay well yesterday I cleaned the carb out and then noticed I had the distributor cap wires backwards.... put it back together and it fired right up! checked the compression and all were at 100

 

[Bondo]

Okay well yesterday I cleaned the carb out and then noticed I had the distributor cap wires backwards.... put it back together and it fired right up! checked the compression and all were at 100

Ayuh,.... That motor is due for a Rebuild,.....

 

[Zhulkk]

well thats no good... :facepalm:

 

[Bondo]

well thats no good... :facepalm:

Nope it ain't,.... How much do ya trust the compression gauge ya used,..??

Generally speakin',..... 140 psi, 'n up is a tight new motor,......

110 to 140 psi is varyin' degrees of a worn motor,.....

Under 100 psi is a rebuildabl;e core motor,.....

Did ya do a leak-down test,..??

That'll tell ya whether the rings are beat, or the valves are bad,....

Bad valves, a valve job might fix,....
Rings is rebuild time,....

 

[Zhulkk]

Its been rainin out but I got out to recheck the compression with another tester. I got close to 120 on them all. Now for the valves, when we first re put them in we had no idea how to tighten them up so that could be a problem :Cry:

 

[Zhulkk]

how hard is a rebuild and how much do the parts cost?