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‘90 300gt V8 surging and smoking

M

Marks1158

New member
Just started doing this. Compression good on all 8. Good impeller. Plugs changed last fall. Tried sea foam. Speeds up and slows both on idle and plane. Smokes a lot when started and when running in “bog” mode if that makes sense. Harder to start than normal. Used to start on 1st key turn once warm, now takes 2-3 tries. Any suggestions on where to start looking? Thanks!
 
Red lever on the electric primer in the correct position ?------Does primer bulb go hard ?----Tried running on a portable tank and hose ??----Check water separating fuel filter ?
 
Hi, it’s a 2 cycle. I’ll try to find the red lever, I have the manual for it. I don’t have a portable tank. Bulb (fuel) is hard, I’ll check oil bulb. Will also check fuel filter.
Thanks!
 
Remove cover in front of carburetors.-----Have assistant drive the boat.----Use a STRONG flashlight and shine into each carburetor when it is surging.----Compare amount of fuel coming up each nozzle.
 
Check the fuel pressure from VRO to carbs. The smoking could be oil side of VRO has problem ot bad oil tank cap. If you try Raceone suggestion, do not run it far as the that motor has a restrictive air box and it will run lean with it removed
 
Thanks all!! Waiting for the weekend to check things. And still trying to decide if I’m brave enough to sit on the back of the boat with my wife driving😳
 
I know there are 8 carburetors.--One supplies only one cylinder.-----I know it is a lot of work to inspect each one.-----Might be something you can do at home.----Check carburetor bowl for leaks / warpage.-----Carburetors are important they are also the oil pump for all the bearings / pistons.----A plugged / restricted carburetor can lead to astronomical repair costs.
 
Got to work on it a little last night. Pulled all the plugs and they looked good. Checked oil tank and found a broken clamp on engine side of the primer bulb. No other leaks found on the engine. Oil tank was very low ( not sure why alarm hadn’t gone off). Emptied it and there was some water in the bottom. Cleaned it and put new oil in. Going to check the fuel tank tomorrow. I suspect water in there. I got a motor flusher, but tried it and no water coming through when I started motor so I didn’t run it long.
 
Update, very little water in gas. Added Heet to help. Pulled plugs again, top of all pistons look good, all the same. Compression on all 8 cylinders is between 116-119. No leakage of pressure. I think I’m ruling out head gasket. . I need to run it at the lake next to see if clamp on oil primer, new/dry oil, and new fuel have made it any better.
Any comments please?
Thanks!
 
Please excuse my ignorance, I know I’m in way over my head on this one…
It has 2 VRO’s. Doesn’t each one feed the 4 cylinders on one side? Would one side of plugs/pistons/ or something show signs of a difference?
 
Update
-have a water tank to run it at home
-disconnected oil tank and now have premix 50:1 in main tank
-replaced head gaskets, no change.
- let all water drain out. Started it for a few seconds, let it cool, did that several times. Still smoking with NO water flowing in it anywhere.
- has to just be too much fuel going to cylinders?
-Manual says VRO’s have a bypass so it will run if either dies. I isolated top one and ran off bottom, then opposite, no change
-put a clear hose on fuel line at motor to see if it’s sucking air, no bubbles
-will idle all day, jumps out of hole like a rabbit, it just has a LOT of white smoke and surges slightly.
-I’m down to thinking it’s a carburetor issue. Going to work on that next.
Any others ideas?
Please!!!
 
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