fouled plugs

[ematz22]

I have a 1988 twin mercruiser 3.7lx's with the Rochester quadrajet. I can't get it to over 3000 rpm. I seems to bog down. I've changed the plugs and they were fouled badly after a couple hours. Since this has happened I've rebuilt the carb, changed points, set the dwell, checked the timing, changed wires, changed coil, adjusted the choke, adjusted the idle mixing screws and can't seem to get it to run right. The frustrating part is that earlier in the season it's run perfect then it started fouling plugs and that's when I changed all those things. Is it possible for the points to go bad that quickly? I haven't re checked the points yet but is that something that can change with little time on the new points? Any one had this problem? I am planning on checking it but was wondering if anyone had a similar problem

 

[Fun Times]

You may want to confirm the fuel pressure going into the carburetor.

 

[achris]

Are the plugs wet or dry fouled?

 

[alldodge]

I have a 1988 twin mercruiser 3.7lx's with the Rochester quadrajet. I can't get it to over 3000 rpm. I seems to bog down. I've changed the plugs and they were fouled badly after a couple hours. Since this has happened I've rebuilt the carb, changed points, set the dwell, checked the timing, changed wires, changed coil, adjusted the choke, adjusted the idle mixing screws and can't seem to get it to run right. The frustrating part is that earlier in the season it's run perfect then it started fouling plugs and that's when I changed all those things. Is it possible for the points to go bad that quickly? I haven't re checked the points yet but is that something that can change with little time on the new points? Any one had this problem? I am planning on checking it but was wondering if anyone had a similar problem

It started fowling plugs, carb was then rebuilt and other things replaced, issue is unchanged. I would run a compression test.

 

[NHGuy]

If the compression test is good,try these items.
Did you set the points with a dwell meter? if not you should. Also does the timing advance? Put a light on it and make sure.
When you rebuilt the carbs did you take any tension out of the secondary springs? They need to be 3/4 turn in from loose. If they are too loose the carb gives too much gas.

 

[ematz22]

Dry fouling.

 

[ematz22]

I didn't use a dwell meter to set the points I used a feeler gage. Like I said it ran the best it's ever run earlier this year. During the winter I replaced the points, cap, rotor, and condenser. I checked the points today I saw that only about half the 2 contact points were touching not mating up so the 2 points completely. Didn't think it was an issue because there was not charing or pitting. I pulled off the points plate and checked the centrifugal advance moves freely. I ran out of time today because it started to rain. I will check the compression which I did this spring and compare results, check the point gap and use a dwell meter, and check the timing. One thing to note is that looking at the timing advance curve is where there is no more advancement past 3000rpm. I am correctly interpreting this? Just seems odd that my acceleration issue lines up with that. Just curious about that.

 

[achris]

Is this happening on both engines? (Yes, the timing stops advancing at 3000rpm)...

 

[ematz22]

No just the one. I have 2 fuel tanks and I can take a suction from either tank so I ruled out bad gas

 

[achris]

Dry fouling (too much soot) can be caused by a few things. The most common is an over-rich carb, which is where you're looking now. The wrong spark plugs can also cause it, as can weak spark and low compression.

As for not exceeding 3000rpm.. It that also only one engine, or does neither exceed 3000? I'm going to ask the obvious. Both are confirmed as being in gear and the props not slipping on one (spun hub or engine coupler)...

Chris......

 

[ematz22]

I have the spark plugs that are the ones stated on the valve cover. The props are not spun. How do you lean out the carb? Neither engine will go higher in rpm its just too much work. Both have to do their share of the work. The plugs in the other engine look good. Are you supposed to be able to get to wot on only one engine on a twin engine boat?

 

[ematz22]

Before it gets real bad the engine in question seemed to surge a little bit like it wants to go. After running like this i suspect the plugs get so fouled that it just won't go above 3000 without bogging down. The more throttle I give it it does nothing. To much throttle eventually causes rpm's to start dropping off until I cut back on the throttle. Also you can smell the raw gas

 

[ematz22]

An auto mechanic told me that if the float level is to high it can cause a rich condition. Any thoughts? I'm ready to get a marine mechanic involved because it's getting frustrating. Just wanted to try everything I can before I start shelling out the big bucks which may or may not solve the problem. That's why I like this forum. Someone out there has the answer. Just have to get me to it

 

[achris]

I have the spark plugs that are the ones stated on the valve cover. The props are not spun. How do you lean out the carb? Neither engine will go higher in rpm its just too much work. Both have to do their share of the work. The plugs in the other engine look good. Are you supposed to be able to get to wot on only one engine on a twin engine boat?

No, you will not get to max rpm on a single engine without changing the prop.

An auto mechanic told me that if the float level is to high it can cause a rich condition. Any thoughts? I'm ready to get a marine mechanic involved because it's getting frustrating. Just wanted to try everything I can before I start shelling out the big bucks which may or may not solve the problem. That's why I like this forum. Someone out there has the answer. Just have to get me to it

Yes, a high float will cause richness. Or a sunk float. Quadrajets can be quite finicky to set up. I believe there are some very good books around, but you have 2 engines. ie, an engine full of swappable parts. Just to help start narrowing down possibilities, have you considered swapping the carbs, see if the problem follows? That would quite quickly rule the carb out (or in)...

Cheers,

Chris........

 

[ematz22]

I'll swap the carbs. If the problem follows the carb that's easy to fix (just one issue) if not then I have my work cut out for me

 

[achris]

I'll swap the carbs. If the problem follows the carb that's easy to fix (just one issue) if not then I have my work cut out for me

At least you will then have ruled out the carb.

 

[ematz22]

Swapped the carbs. Problem followed the carb. Wouldn't go above 3000 rpms. Fouled the plugs in 10 minutes. Now to figure out what's wrong with the carb running rich

 

[achris]

Needle and seat or a flooded float. Or a jet has 'unscrewed' and now you have a big hole where there should be a smaller hole... At least you know for sure where the problem is. :thumb:

 

[ematz22]

Got another carb rebuild kit and adjusted the float down. Does anyone know the reason for the difference between the needle valve seats? One has slots and one doesn't.

 

[ematz22]

Rebuilt carb installed. Same problem. Not sure what to do at this point