742B-glowing exast pipe, muffler, and exast manifold

[Collisioncenter]

I have been doing some much needed maitenence to my 742b lately. I just checked the timing belt, reset the idle settings and the High speed setting. Installed new belts and removed the muffler drain. After running the machine at wide open, in just a matter of a couple minutes the exast pipe and manifold began to glow. It feels that I have good flow of exast out of the muffler so I don't think that the muffler is restricted. Im curious to know if this is somewhat normal or if there is something that I should be addressing here. Thanks for your time

 

[Tazza]

Sounds like you are running lean causing the exhaust to be getting too hot. Are you sure the timing is also correct?
I'd be careful running it like this too long, that much heat really isn't a good thing.

 

[Collisioncenter]

Sounds like you are running lean causing the exhaust to be getting too hot. Are you sure the timing is also correct?
I'd be careful running it like this too long, that much heat really isn't a good thing.

Timing is set at 5 degress BTDC at idle (850-950rpms) with a mechanical advance of 10 degrees at wide open (2800rpm). Everything seems to be operating normal. This thing was originally set at about 10 degrees BTDC at idle before I adjusted it. Plus I never had any problems after I readjusted the engine speed settings until 2 days later. It seems to start a little harder now than it did previously. And somewhat lacks power. Engine operating temps are completely normal. I haven't done anything to the carb, as Ive been told there is very little that ever goes wrong with them. Im not sure I really want to tear into that as 1: Im not sure thats the problem. and 2: From what Ive been told there quite a challenge to rebuild (not to mention kinda pricey). Any other suggestions?

 

[craigb93]

Timing is set at 5 degress BTDC at idle (850-950rpms) with a mechanical advance of 10 degrees at wide open (2800rpm). Everything seems to be operating normal. This thing was originally set at about 10 degrees BTDC at idle before I adjusted it. Plus I never had any problems after I readjusted the engine speed settings until 2 days later. It seems to start a little harder now than it did previously. And somewhat lacks power. Engine operating temps are completely normal. I haven't done anything to the carb, as Ive been told there is very little that ever goes wrong with them. Im not sure I really want to tear into that as 1: Im not sure thats the problem. and 2: From what Ive been told there quite a challenge to rebuild (not to mention kinda pricey). Any other suggestions?

Any chance the balancer has a rubber center that has slipped and the timing is actually late? You said it ran better when set at 10 BTDC, move it in that direction to aleviate the lean heat. Buildup in the carb jet from ethanol/gas will make the mixture lean. Give it a good slug of fuel conditioner like Stabil Marine, 3-4x the label amount to start then steady after that. If you want to check the validity of the TDC mark make a piston stop out of an old spark plug and a bolt. Take the plugs out, screw in the stop tool, turn the crankshaft one way until it hits the stop, make a pencil/crayon mark at the timing pointer, turn the crank opposite until it hits the stop, make another mark. TRUE TDC is in the center of the two pencil marks. Hope it is also the same as the factory mark. If not use the center of the pencil marks to time the motor.

 

[jerry]

Old machinist has posted a link to the service manual for your machine. If it has the ford engine the initial timing is 12 degrees btdc. use the search function here to find the link. when all the advances are working on those engines the timing is way more advanced than you would expect. if you use firefox you have to hit search twice before it comes up with results.

 

[Collisioncenter]

Old machinist has posted a link to the service manual for your machine. If it has the ford engine the initial timing is 12 degrees btdc. use the search function here to find the link. when all the advances are working on those engines the timing is way more advanced than you would expect. if you use firefox you have to hit search twice before it comes up with results.

The Timing is set according to the service manual, as I own one for this machine. The timing jerry is refering to is for the old original "742" with the ford engine. The "742B" has the updated Mitsubishi motor, which is what mine has. The service manual says to time it at 5 degrees BTDC idling somewhere between 850-950 rpm. Then run it wide open at 2800-2900 rpm with the vacuum advance unhooked and it should mechanically advance to about 15 degrees. Which it does and all of this is correct! I haven't pulled the plug on number one and checked it in corilation to the rotor location yet....Thats tomarrows project. The problem is for the first night that all of this was set I had no trouble at all with the exast manifold and exast pipe. It was the second night that I was working on it that this gave me trouble. Im beginning to think that its in the carb. I might get ambitious and do a compression check and a leakdown check later...I'll c. Let me know if there is anything else anyone can think of! Thanks again

 

[catfish]

The Timing is set according to the service manual, as I own one for this machine. The timing jerry is refering to is for the old original "742" with the ford engine. The "742B" has the updated Mitsubishi motor, which is what mine has. The service manual says to time it at 5 degrees BTDC idling somewhere between 850-950 rpm. Then run it wide open at 2800-2900 rpm with the vacuum advance unhooked and it should mechanically advance to about 15 degrees. Which it does and all of this is correct! I haven't pulled the plug on number one and checked it in corilation to the rotor location yet....Thats tomarrows project. The problem is for the first night that all of this was set I had no trouble at all with the exast manifold and exast pipe. It was the second night that I was working on it that this gave me trouble. Im beginning to think that its in the carb. I might get ambitious and do a compression check and a leakdown check later...I'll c. Let me know if there is anything else anyone can think of! Thanks again

If it ran fine the first night, then started getting the hot exhaust, I would check your distributor hold down to make sure its tight. If you didn't get it good and snug it may have "walked" a little and the timing is off again. The hard start starting sounds like the timing is off.

 

[Collisioncenter]

If it ran fine the first night, then started getting the hot exhaust, I would check your distributor hold down to make sure its tight. If you didn't get it good and snug it may have "walked" a little and the timing is off again. The hard start starting sounds like the timing is off.

According to the timing light, the marks on the engine and the mark on the crank pulley the timing is on, has been on and continues to be on. Its good and tight and has not retarded or advanced itself. I don't think that timing is the issue at hand. Im gonna check it one more time tomarrow, along with checking the rotor location in the cap, in relation to #1 TDC.

 

[Collisioncenter]

According to the timing light, the marks on the engine and the mark on the crank pulley the timing is on, has been on and continues to be on. Its good and tight and has not retarded or advanced itself. I don't think that timing is the issue at hand. Im gonna check it one more time tomarrow, along with checking the rotor location in the cap, in relation to #1 TDC.

After careful consideration, I've discovered my problem. The key had sheared off the crank pulley and rotated about 30 degrees. So when I timed the motor up I was actually retarding the timing by about 40 degrees. Its amazing that it would even start. After the timing was corrected, the thing starts right up and runs great! No glowing exast after about a 10 min wide open cycle!

 

[Tazza]

After careful consideration, I've discovered my problem. The key had sheared off the crank pulley and rotated about 30 degrees. So when I timed the motor up I was actually retarding the timing by about 40 degrees. Its amazing that it would even start. After the timing was corrected, the thing starts right up and runs great! No glowing exast after about a 10 min wide open cycle!

Glad you found the problem!
A crank key.... Not something i'd have suspected, nice catch.