I put my IM heads on finally and am having some problems now. My throttle response is slower but it would still turn 4200 oow but I have no power. Put it in today and it wouldn't turn over 2400 rpms. Valve lash was set by Cody's way and then I tried it per Briggs by going off TDC. What is yalls opinion? Could I be pulling in air through a damaged gasket? Would it cause that? Any help is appreciated

Check the compression.

You set the valves Cody's way, and then Briggs way. How much difference was there in the lash? There really shouldn't be any. From the info you gave, I would be guessing you screwed up the lash. Hopefully you didn't damage the cam.

Did you set the valves on the compression stroke?

Compression test will tell of a bad head gasket and you prob would hear it


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Whats the best way to check.compression? Asking because I dont have a ton of fancy tools. I set it per Codys way and when the throttle was lagging I double checked it per Briggs method. I ran the boat for at most 20 yards when I realized something wasn't right.

If the cam is damaged it'll be okay because I'll be replacing it soon

When you double checked the lash, was it spot on or did you have to change it again?


You can borrow a compression tester from your local auto parts store. Pull the spark plug, insert the fitting on the tester into the spark plug hold, hold the throttle WOT, and turn the starter until the dial quits going up. Just a few revolutions should suffice. Make sure you remove the plug and/or the plug wire on the other side before testing so the motor doesn't fire up on one cylinder.

Lash was spot on. No adjustment needed. And cool. I will do that asap. What does it sound like to you CB?

Compression test will also tell you if valves are holding. Did it backfire any?


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No backfire at all. It really has me stumped on what the hell is going on.

I bet the IM heads are the problem get Cody to fix 'em

If lash was spot on, im relatively confident that part is okay.

I'd proceed with a compression check and go from there. If those numbers are bad, you'll need to do a leak down test.

Are you firing on both cylinders?

Yes it is firing on both cylinders. Its idling great. Idle is set at 1100. The power just isnt there.

Had one a while back firing on both, but wouldn't run on both. Pull plug wire to see if it'll still run on one cylinder. My case ended up being blown gasket between cylinder and push rods. Couldn't hear it while running, but had no power.

Same problem on mine Camo. Ran compression test on it this morning and it failed. Tore it down and found that a head gasket was damaged.

Head gasket will do it


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Just came across this. Glad you go it figured out. Once you have it dialed in, let me know how it performs

Think of it this way, 2400rpm with one blown gasket, so now you may get 4800

When you go for round two, You need to take some sand paper and rough up the face of the cylinder a little, this will help the gasket "grab" the face. If you will notice the factory surface is very smooth and almost mirror like, not good when you want a gasket to seal.

Actually did that Will. Cleaned all the old gasket off and scuffed the surface. My next question tho is do y'all put a sealant along with the gasket. I didnt use a sealant because my step-dad said it wasn't necessary. Im asking because I dont want to pull the dang thing apart again for another simple fix.

No sealant, in fact clean it with alcohol before you put on the new gasket.

I use copper spray on the head gaskets. Don't know if that is a good idea or not, but I haven't had any issues and have done it this way on all the motors I've put together.

do not ever sand ur head or block surfaces ever.

Why would that be Richard? Just curios. It wasnt a heavy sanding. Just a slight scuff. We do that on just about every surface that has a gasket on it on the equipment around the farm and vehicles.

sc. a alum head and block most call for a 30 to 50 ra finish. a finish that is hard to see with a eye. for a proper seal. by sanding the surfaces u could be putting in as high if not higher 100 ra. not good what ur are doing is intoducing a path way for gases to pass thru. u don't want a head gasket. as Will says that bites. during a heet cycle a head gasket moves causing what is called scuffing. which is normal. a high ra or sanded rough surface over time will cause a delaminating of the head gasket seal. causing a head gasket leak. i always clean the surfaces with a plastic scraper and howes lubricant to remove gasket material. never use a die grinder with a rolox pad a metal scraper or razor blade.

You do make sense. Just for clarification so I don't look like a total fool I did not use a die grinder or any highly abrasive material. I did use a 600 grit sandpaper. Thanks for the info Richard. It is nice having a forum dedicated to idiots like us who love running a lawnmower motor and constantly pushing them to the limits. Its also nice that there are some of y'all that are extremely knowledgeable about these motors

sc. i might of went over the top. but be careful dressing up a head or block surface. deep scratches cause problems down the road.

rn. I understand why you say not to scuff the surface, it makes since no doubt but that's the way I've been told on many different motors. What about the case gasket, what's the best way to "try" to fix that leaky bastard?

I've got mine pulled right now bout to put in a new clutch, thought I might just dip the bottom half of the motor in a tub of silicone...

Thanks for the help fellas. I put the motor back together this morning and the power is there. Now its time to eat CDMs spank new PD rig this weekend