Big problems with my Bigtwin? Running super rich, won't WOT (see pics, video)

[BonairII]

Took my Bigtwin 35hp on the water today. Starts fine and idles well, but will not throttle up. Could only go about 10mph on half throttle. If we gave it more throttle it bogged down.
Took out the plugs and they were wet, of course. They were J4 plugs(J6 is the correct plug, I think)
There are a couple issues going on. First, the gas tank is leaking air(pressurized system). I could see gas/air spitting out a bit under the corner of the handle to the gas tank.

The second issue: I seated the low speed needle and backed it out a turn and 3/4 to start the motor and it ran fine as we slowly putted out to deeper water in the river....But I had to turn it all the way in to get the motor to throttle up a bit
BTW: Is it safe to assume that the low speed needle is the pointed one and the rounded-end needle is the high speed needle?

Checked out the(bad) pic of the low speed needle and tell me if it looks like the end has been flattened out (PO's kids may have seated it too firmly)
Haven't checked spark yet, but compression was 90psi for both cylinders

Went thru 3-4 gallons of gas in a pretty short time btw.
Also notice black crud(see pic) pooling in the back of the motor lower shroud. I'm thinking that the motor has been run rich for quite awhile.
http://www.youtube.com/watch?v=SuF0crDwlmM

http://www.youtube.com/watch?v=SuF0crDwlmM

I need any help you can give cause I'm going to work on it tomorrow(Sunday) and the boat is docked 25 miles away at my sister's house....and I need to have all the tools/info I need with me.

 

[tx1961whaler]

Re: Big problems with my Bigtwin? Running super rich, won't WOT (see pics, video)

Starts well, idles well, good compression, probably good spark (it wouldn't start or idle well otherwise). If I were to guess it would be a clogged main jet on the carb. Also make sure the carb is synched to the ignition properly; the little roller on the carb linkage should not start to open until it is lined up with the two little lines on the magneto plate.

 

[BonairII]

Re: Big problems with my Bigtwin? Running super rich, won't WOT (see pics, video)

I'm a bit of a noob to know what a "little roller on the carb linkage" is. Any chance you have a pic of what you're referring to? Would any of what you speak of cause it to run super rich? Does the needle in the pic looked like the end is flattened out at all?

 

[1946Zephyr]

Re: Big problems with my Bigtwin? Running super rich, won't WOT (see pics, video)

Yes, the pointed one is the low speed and the blunt one is the high speed. Your settings are 1 1/2 turns out on the low speed and 3/4 turn out on the high speed. I see the tip of the low speed is gone, but at least the chamfer looks good and straight. Often times, if the low speed is over tightened in the seated postion, the tip will get stuck and get left in the oriface that it seats into. You might need to look into that.
How do the coils look in that old gem? If you're coils are bad, then you're most likely running on one cylinder. Look for cracking on the insulation of the coils and yes you should run a J6C plug, even though it calls for a J4. J4C's are absolutely worthless for performance. That motor actually calls for a J4J, but those were actually a lot better than the newer J4C.

 

[cr9c1]

Re: Big problems with my Bigtwin? Running super rich, won't WOT (see pics, video)

Yeah that high speed needle doesn't look right at all to me. You should check spark though, I can't really tell but ti sounds to me like it may be operating on one cylinder. Usually they start hard when that happens but its hard to say. Have you ever changed the coils, points, and condensers in it?

The pressure tank leaking can't be good either, since the pressure is what pushes the fuel into the engine.

 

[BonairII]

Re: Big problems with my Bigtwin? Running super rich, won't WOT (see pics, video)

Haven't really checked anything yet. Checked compression only. I've read so much here about engine repair that all the info is all garbled in my head on what to be checking (and HOW to check it). I'll get a spark check gauge tomorrow. Is there a simple way to check to see if I'm running on only one cylinder?(or will the spark gauge let me know).
Would running on one cylinder cause me to go thru so much gas at only half throttle? BTW: when I disconnected the air/fuel line connector from the motor, gas drooled out the nipple for a bit(possibly draining the carb?). That can't be normal, can it?
I brought one of the plugs home...it's a Champion J4C
BTW: I tried pumping the tank while we were riding along and it seemed to bog the engine a bit when I built up some pressure.

Almost forgot. What gap should the spark be able to jump?

 

[tx1961whaler]

Re: Big problems with my Bigtwin? Running super rich, won't WOT (see pics, video)

The simple way to see if it is running on one cylinder is to pull the spark plug wires off one at a time when it is running. If you pull one off and the engine does not change RPMs at all, then that cylinder is not firing. Should jump a 1/4" gap with a bright blue-white spark using a spark tester.

 

[BonairII]

Re: Big problems with my Bigtwin? Running super rich, won't WOT (see pics, video)

Update: Checked spark...it seems good. It jumped 1/4 gap and managed to give me a bit of a shock in the process. I also pulled each plug while it was idling and the engine stumbled...so both cylinders are firing. I ran an entire can of Seafoam w/ 8 gallons of gas. I also sprayed about a 1/2 can of carb cleaner(small/medium shots while motor was running on the water). New plugs seemed to make it a bit more peppy. I fixed the air leak on the fuel tank also, so low fuel pressure isn't a problem.
Boat seems to be 95% on plane. Goes about 15-18 mph. It guzzling a ton of gas IMO.

Now I'm thinking that the boat is overpropped...which makes me wonder if THAT is what is keeping the boat from revving OR is this just and ADDITIONAL problem. When we made some tight turns, and the prop ventilated and the RPMs shot up so now I know that the motor WILL rev up....which of course, also makes me wonder if the motor is too short for the boat.

High speed needle still has to be turned all the way so motor doesn't stumble at WOT.

I'm getting a bit frustrated.
Anyone have any advice on my next course of action?

 

[Fishgeek]

Re: Big problems with my Bigtwin? Running super rich, won't WOT (see pics, video)

I'm a bit of a noob to know what a "little roller on the carb linkage" is. Any chance you have a pic of what you're referring to? Would any of what you speak of cause it to run super rich? Does the needle in the pic looked like the end is flattened out at all?

I have a '56 BigTwin 30 that I refurbed with the help of a friend...but mostly with the help of a Seloc's repair manual. I got mine at the local library but if I ever need again I'll spend the $20 to buy my own. I think its worth the money.

 

[tx1961whaler]

Re: Big problems with my Bigtwin? Running super rich, won't WOT (see pics, video)

Was the carb rebuilt, as in disassembled, soaked, main jet cleaned, every passageway cleaned and blown out with carb cleaner and air, welch plugs removed and idle air circuits cleaned, and a new carb kit installed? That high speed needle doesn't look right to me; most I've seen have a needle end to them. But I will say I can't remember taking apart a 35 of that vintage before.

 

[BonairII]

Re: Big problems with my Bigtwin? Running super rich, won't WOT (see pics, video)

PO said carb was rebuilt by a mechanic. I notice that the main carb gasket looks a bit large(lot of gasket hanging out around the seam), so I'm guessing if it was somewhat 'rebuilt'....that it was just a cob job. The packing nut on the low speed needle doesn't hold the needle firmly and the needle rotates it way out if I don't keep an eye on it.
Oddly, I have the low speed needle 1 1/2 turns out to start/idle the motor....but I have to pretty much seat the needle when I'm at WOT. Should the low speed needle have ANY effect of performance when motor is at WOT?? If I back out the high speed needle at all(from it's fully seated position) at WOT the motor starts to bog/stumble.

 

[BonairII]

Re: Big problems with my Bigtwin? Running super rich, won't WOT (see pics, video)

Anyone know where I can find new needles for my motor? And also where to get the carb rebuild w/ float kit? It's a 1958 Bigtwin 35hp.

 

[tx1961whaler]

Re: Big problems with my Bigtwin? Running super rich, won't WOT (see pics, video)

The high speed needle is probably OK, since 1946Zephyr said it is. He knows this vintage better than I do.
The carb kit with a float is OMC PN 0396701, or Sierra 18-7222. iboats has the Sierra kit, but it is not listed under the 35 hp listing. The OMC part is at marineengine.com and also cross-references the Sierra part. I'd personally go for the factory OMC kit, because I think your carb has some problems and it should come with an instruction sheet. The Sierra ones usually don't come with anything.

 

[BonairII]

Re: Big problems with my Bigtwin? Running super rich, won't WOT (see pics, video)

Does the carb kit come w/needles and/or the packing nuts? This will be my first carb rebuild...any advice other than taking pics of the carb and linkage for reference?
The welch plugs are what scare me most. I've never dealt with them before and don't know how to take them out or reinstall new ones.

Talked to the PO about the motor issues...and he seems genuinely stumped. Said he and his boys ran the boat last week and were going right along at about 30mph.
I'm going to run the motor with the cowling off tomorrow(my 14 yr old will be doing the driving while I monitor the motor). Can I run the motor with the airbox off? I want to mist the carb w/ premix and see if the motor bogs and I'm not sure I'd be able to squirt the premix thru that small hole in the airbox.
Anything else I can try while the motor is on the water to rule things out?

 

[kfa4303]

Re: Big problems with my Bigtwin? Running super rich, won't WOT (see pics, video)

Hi BonairII. Read this link and you'll have that 'ol Big Twin back up and running in no time. The Hi speed needle should have the blunt end, while the lo speed needle is pointy. Make sure the brass nut/bushing the needles pass through is snugged down tight once the needles are set. This wil prevent the needles from backing out or wiggling loose while under way. "Rebuilding" a carb is easy. It really just entails thoroughly cleaning the car and replacing all of its gaskets. Plenty of links here in the forums on how to do it.


http://www.duckworksmagazine.com/04/s/columns/max/24/index.cfm

 

[1946Zephyr]

Re: Big problems with my Bigtwin? Running super rich, won't WOT (see pics, video)

New carb kits will come with packing. When you replace the packing, be sure to put the nylon washer in last, because this will prevent the packing nut from chewing up the packing and it will help compress the packing better. Once the packing is in, you should be able to tighten the nut enough to stop the needle from vibrating out. You don't want to tighten them too much, or you won't be able to turn it.
If you need a new low speed needle, you should be able to find one at one of the salvage yards listed in the top secret file. Your high speed looks good, but who knows how well your low speed will work, with the tip gone. I have actually heard of people having their needles turned on a lathe, to obtain a nice clean chamfer. Make sure you look inside where the low speed needle goes to make sure the tip isn't stuck inside. I've seen this before and it'll drive you nuts trying to get your motor to run.

 

[BonairII]

Re: Big problems with my Bigtwin? Running super rich, won't WOT (see pics, video)

Update: i MAY have solved my WOT problems. Today I ran the motor with the cowling off to see if I could tinker with it while it was running. I tapped on the carb with the back of a screwdriver in hopes that maybe the float was stuck and it would break free. No luck there, but 10 minutes later the float bowl partly separated from the carb. 3 of the carb screws that hold the float bowl were loose a hell and the 4th screw at the back of the carb was missing! Of course, I didn't have a short screwdriver to be able to tighten them up....so I had to use my trolling motor to get to shore. Fortunately, I kept all motor testing to within sight of my sisters house.
I'm guessing that the float bowl has been leaking air all this time and allowing too much fuel into the carb....which would explain why I had to keep the high speed needle completely seated at WOT. Am I correct, in this thinking?

 

[tx1961whaler]

Re: Big problems with my Bigtwin? Running super rich, won't WOT (see pics, video)

Update: i MAY have solved my WOT problems. Today I ran the motor with the cowling off to see if I could tinker with it while it was running. I tapped on the carb with the back of a screwdriver in hopes that maybe the float was stuck and it would break free. No luck there, but 10 minutes later the float bowl partly separated from the carb. 3 of the carb screws that hold the float bowl were loose a hell and the 4th screw at the back of the carb was missing! Of course, I didn't have a short screwdriver to be able to tighten them up....so I had to use my trolling motor to get to shore. Fortunately, I kept all motor testing to within sight of my sisters house.
I'm guessing that the float bowl has been leaking air all this time and allowing too much fuel into the carb....which would explain why I had to keep the high speed needle completely seated at WOT. Am I correct, in this thinking?

The carb is full of air all of the time, except for the float bowl. If the float bowl gasket was loose, then it would have been leaking gas like crazy. BUT, if the bowl was not tightened down properly, that can make the venturi tube gasket not seal properly to where it pulls gas through the main jet.

 

[BonairII]

Re: Big problems with my Bigtwin? Running super rich, won't WOT (see pics, video)

that can make the venturi tube gasket not seal properly to where it pulls gas through the main jet.

Are you saying that the venturi SHOULDN'T be pulling gas thru the main jet? Would that explain why I'm running thru gas like crazy??

Took it out again today. I tightened up all carb bolts and replaced the missing bolt, Got it up to 20mph which is about a 5mph better than last outing. Noticed fuel lines are dry rotted at the quick disconnect end. Won't be able to replace til tomorrow.

 

[BonairII]

Re: Big problems with my Bigtwin? Running super rich, won't WOT (see pics, video)

Update: Have made a LITTLE more progress on the motor. I changed out the fuel lines(from the disconnect to the carb/crankcase nipples)...the line was brittle and broke off easily). Motor seemed to be a tad happier with the new line. Got it to 23mph for a short time today, then it ran 20-21mph after that.
I opened up the throttle(w/motor off) and noticed that the rear butterfly in carb really wasn't opening much. So I moved the throttle rod collar down the throttle rod(toward back of motor). Now when I throttle up the butterfly opens fully. Is this correct or do I need to somehow adjust timing also?

I took off the carb and opened it up. Everything was clean as a whistle, although the cork float looks ugly (see pic). I also noticed that the float wasn't perfectly level. It was was just slightly pitched downward(while carb was upside down). I wonder if that small incline would cause the float needle to NOT seat properly. Also noticed that the float valve and seat nut has NO rubber seat in the assembly. Since I don't see it listed in the parts diagram...is it safe to assume that there shouldn't be a rubber piece in the seat that I need to pick out and inspect?

I DID notice that the high speed nozzle(not the high speed mixture needle) didn't seem to be snug in the carb...It started turning as I touched it. What symptoms would a loose nozzle cause? The nozzle was clean and clear(incl the small passage in the side of it).

I did NOT notice the tip of the low speed needle inside the carb, so I'm guessing that the needle is just dented and nothing broke off.
BTW: There was NO gasket between the carb and the motor...do I need one there? Also, is the gasket between the carb and airbox important? Would a leaking gasket there cause any performance issues?