Compression Question 91 200GT and a miss need alittle HELP..

[imthemedic]

I just purchased a 1991 Stratos with a 200GT Johnson. I did a compression test and it read 75 across all 6. It did start and run alittle ruff but the fuel sysytem had obvious issues. I brought it home and drained both tanks, replaced all fuel lines, filter, water seperator, and bulb. I filled the tanks and added Sea Foam. I took it to the lake yeasterday for the first time and fired right up. I noticed it had a miss kinda like a cough? It missed hard enough to cause it to stall when in gear and idleing at 650rpm. Miss is pretty consistant every few seconds. When trying to accelerate it just doesn't want to get up on plane like it just bogs. I have to slowly ease into the throttle and try to get up on plane. Once there it run ok and I can hear or feel a miss. It only was able to get to 50mph GPS at 5200rpm. I think it should have alot more top end than that. I have no jackplate and run a 24" Raker. Someone please give me some guidance. PLease don't tell me I bought a bad motor.

 

[kenmyfam]

Re: Compression Question 91 200GT and a miss need alittle HELP..

Well 75 psi is a little low but don't take that to heart yet. Compression testers vary so it would be wise to try it with a different one. The fact that compression is even is a good thing.
You need to check
Spark to all cylinders
Fuel delivery
Spark plug condition.

We can all go from there.

 

[imthemedic]

Re: Compression Question 91 200GT and a miss need alittle HELP..

The plugs were new and the fuel system was replaced. Not sure about spark. I was affraid to check by lying the plugs against motor. I thought it might burn something up. I have seen shops use the boards where you can see spark jump across. I didnt know if that was the only safe way not to fry the electronics.

 

[kenmyfam]

Re: Compression Question 91 200GT and a miss need alittle HELP..

The plugs were new and the fuel system was replaced. Not sure about spark. I was affraid to check by lying the plugs against motor. I thought it might burn something up. I have seen shops use the boards where you can see spark jump across. I didn't know if that was the only safe way not to fry the electronics.

Get yourself a $10 spark tester from your local auto store.
Please elaborate on "the fuel system was replaced"
The plugs being new means nothing. What condition are they in now after running the motor ????

 

[imthemedic]

Re: Compression Question 91 200GT and a miss need alittle HELP..

I will check tomorrow on the plug condition and I will call advanced or somewhere to see if they sell a cheap spark tester. I will try to get all that info and get back to everyone. I also am going to use a friends Compression tester if he remembers to bring it lol.

 

[kenmyfam]

Re: Compression Question 91 200GT and a miss need alittle HELP..

I also am going to use a friends Compression tester if he remembers to bring it lol.

Call him before he leaves to come over.

 

[imthemedic]

Re: Compression Question 91 200GT and a miss need alittle HELP..

Update, I borrowed a couple of compression testers. The new numbers are 90-92 across the board. I tested the spark and it could jump across atleast a 1/4" gap it read 10 on the tester (what ever that means). Top plugs looked a light coffee stained, next 2 were a little darker with some carbon build up, the last two were a little wet with lots of residue. When I ran it on the hose the miss seamed like it was back fireing through the carb. I could occationaly see a small shot of white smoke come out of the bottom of the breather after the miss. After the motor warms up a bit it seems to be a little less rough, but still a slight miss.