I am not sure you have a problem. The split fire plug is a projected nose (tip) plug and is giving a more thorough burn. Notice how much further out the ceramic projects from the end of the plug? The champions do not. You need to be running the same type of plug in both engines, then compare. I don't particularly mind the black plug color unless it is giving a poor result. Was there a performance or soot problem?

Dennis Moores book covers projected tip plugs vs standard quite completely. I'd recommend buying it as well. I run the project tip A/C plus myself.

BT

Iggy, thanks for all the advice.

Blue Thunder; I ran split fire in both engines, and the split fire came out after 30 hours of run time looking just like the Champions do, very black.

The performance issue is the plugs fouling out. When they look like this, first one, and then the others in quick succession foul out, and then the engine loses power, and eventually quits.

I just installed A/C plugs, so I want to rebuild the carb so I can see how long they will run after.

Here's what they are in.

Don't forget to epoxy the base plugs under the bowl

Nice pics BTW.

Why don't you swap carbs to see if the problem follows the carb?

When you get the rebuild kit, compare the accelerator pump from the carb to the one in the kit. I believe Merc is now recommending using the auto style pump instead of the marine or hi-perf pump that came in the original marine Q-jets. You can still get this hi-perf pump from Edelbrock. I think the number is 1982.

I'm thinking INSPTECH hit the nail on the head. Q-jet's are notorious for leaking from the base plugs. I'm betting fuel is leaking by and causing an over rich condition. Epoxy those, treat it to a rebuild kit, and you'll hopefully be back in business.!

Inspectect is absolutely correct. Use a good 2 part epoxy for that. Thats a major cause of q-jet problems. And even if they are already epoxyied, re-apoxy them.

Leaking well plugs was a big problem on the older Q-jets with brass plugs. The newer 4MV's (post 1980) don't really have that poblem. Some do leak, but not like the older brass plugs, IMHO.

I have a brand new 750cfm marine Holley dual feed, double pumper carb. Used only ......3 hrs...yes , almost brand new.

Only $325.00 with K&N air filter.....

Sheikman

If the plug leaking were the problem, would the burn look so uniform? I'd think some plugs would be blacker than others due to the non atomized fuel "dripping". Just curious because my 1988 qjets are not epoxied to my knowledge.

BT

I'm guessing the carbs are circa 1983, and "close inspection" doesn't seem to indicate any leaking from the bottom side. It doesn't look like brass plugs, I would almost say a lead material.

When I ran the split-fire plugs, they looked just as uniformly black as the Champions in the picture do. Started fouling out at 30 hours.