Hard hot start on 340 monsoon

[h2oskidude]

I would be interested to hear from people having the hard hot start problems on monsoons 340's. Next time try and pull the pin to disengage the transmission and push the throttle 1/2 to 3/4 down like you would do for a flooded start and see what happens. I have been able to get mine started this way but I also did some further checking and found that I have 3 cylinders with compression below 85psi. I have been running 100 octane aviation fuel.

[bigD]

Running a higher octane then your engine requires is a waste of money and in some cases cause a performance Decrease. High lead av gas can screw O2 sensors your injectors and Cats....If you have them.

Av-gas is OLD school hot rodder stuff that worked back then in old high compression carbed or blow engines because it burns SLOWER and help prevent detonation/pre-ignition. I ran leaded Sunoco or trick in my Chevelle mixed with unleaded 91 when it was one of those nights and I needed it, and still use oxygenated Sunoco in the dirt bike but I have to cut it with 91 or performance suffers from too high of an octane and I don't want to mess with the carb tunning that much. I think Av-gas is really hard on your oil also. I'm not sure but I THINK it was due to high sulfur content or something,

Other then using less than optimal fuel you have some other issues that I can't diagnose

[skier92]

Just curious, what is the compression in the other five cylinders?

[h2oskidude]

Just curious, what is the compression in the other five cylinders?

Cylinder Compression

1 - 30

2 - 155

3 - 155

4 - 85

5 - 170

6 - 145

7 - 40

8 - 110

I have done some internet searching and found that GM uses to different heads on the 350 block one is stamped 10239906

and the other 12558062. From what I am finding out is the the 906 heads have a problem with the exhaust seats and are hardened and seam to crack. I guess they used these heads on trucks. The 062 were put into cars. All of my compression leak is going out the exhaust valve. and I have the 906 heads.

[Baddog]

Just curious, what is the compression in the other five cylinders?

Cylinder Compression

1 - 30

2 - 155

3 - 155

4 - 85

5 - 170

6 - 145

7 - 40

8 - 110

I have done some internet searching and found that GM uses to different heads on the 350 block one is stamped 10239906

and the other 12558062. From what I am finding out is the the 906 heads have a problem with the exhaust seats and are hardened and seam to crack. I guess they used these heads on trucks. The 062 were put into cars. All of my compression leak is going out the exhaust valve. and I have the 906 heads.

So now what?

[h2oskidude]

Running a higher octane then your engine requires is a waste of money and in some cases cause a performance Decrease. High lead av gas can screw O2 sensors your injectors and Cats....If you have them.

Av-gas is OLD school hot rodder stuff that worked back then in old high compression carbed or blow engines because it burns SLOWER and help prevent detonation/pre-ignition. I ran leaded Sunoco or trick in my Chevelle mixed with unleaded 91 when it was one of those nights and I needed it, and still use oxygenated Sunoco in the dirt bike but I have to cut it with 91 or performance suffers from too high of an octane and I don't want to mess with the carb tunning that much. I think Av-gas is really hard on your oil also. I'm not sure but I THINK it was due to high sulfur content or something,

Other then using less than optimal fuel you have some other issues that I can't diagnose

Thanks for the info. The only reason I was using the AV-gas was I fly for a charter company and was able to get it as cheep as car gas. I fill up a 300 gal tank at my home and use it through the summer. I was told it would not degrade as fast a auto fuel with have it sitting in the tank all summer. Does the moonson have O2 sensors? and where at if they do.

[h2oskidude]

Just curious, what is the compression in the other five cylinders?

Cylinder Compression

1 - 30

2 - 155

3 - 155

4 - 85

5 - 170

6 - 145

7 - 40

8 - 110

I have done some internet searching and found that GM uses to different heads on the 350 block one is stamped 10239906

and the other 12558062. From what I am finding out is the the 906 heads have a problem with the exhaust seats and are hardened and seam to crack. I guess they used these heads on trucks. The 062 were put into cars. All of my compression leak is going out the exhaust valve. and I have the 906 heads.

So now what?

Find some new heads. Summer is almost over so I will wait till boating season is over. If I am going to have to put on new heads I would like to find out what Indmar does different between the Moonson 340 and the Hammerhead 383. I am not sure if it is just different heads or if there is a different cam with it also. I anyone has any infor or in put I am all ears or eyes in the case. Thanks Dave