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1971 Harley sportster. Ive been trying to fix the issue I have where I lose power in forth thought it was a carb issue changed the jets because the bike came from ca and I live in Colorado but I did a compression test and it has none I got 90 in front and 30 rear, it starts up good and runs decent first through third but fourth just loses it. What should I do now? Ive never had to mess with compression issues. Any suggestions?
Ensure a Big Twin Mechanic did Not adjust the pushrods!!First..
Don't laugh...Seen it back when we had a Shop!!! Guy was adamant that he adjusted Pushrods on his Stock Shovelhead ...by the Book.
Sadly it was a Sheet Metal Copy, Ironhead!!
Last edited by Racepres; Sep 22, 2024 at 06:48 PM.
Agree with Racepres, start with checking the pushrods adjustment. But check and adjust them cold because the cylinder grows taller when they heat up so if you set them hot the valves won't close when cold.
Did you check compression with the engine hot or cold? Did you hold the throttle wide open? The 90 psi isn't too bad, but 30 is bad, surprised you say it runs decent in 1st through 3rd.. If you have a way to put some compressed air in the cylinders one at a time while the valves are closed (remove the pushrods it necessary) and see if the air comes from the intake or exhaust.
Is it smoking out of the exhaust or using oil? Check the spark plugs for lots of carbon buildup (unless they are new). The old iron Sportsters were hard on valve guides, I've seen valve guides bad enough that they allowed oil down the stem so that the back side of the exhaust valve will build up so much carbon it can hold the valve partially open. You could pull the rear exhaust pipe and see how the valve looks. If you do, take a picture(s) and post it.
Save yer sanity!!!! Jump in there and get yer hands dirty. Having a Factory Service Manual is highly recommended. Pull the top end off. Inspect and measure cylinder bore for oversize pistons. Replace with WISECO 10:1 forged pistons. Disassemble the heads and clean them up. Replace all valve guides and have the no-lead valve seat conversion done. Might wanna take em to a competent machine shop for surgery. Reassemble with copper .015 head gaskets. Spray the new head gaskets with Permatex Copper Sealant. HAVE FUN!!!!
^^ Why, in the Wide World of Sports, is the Folks at the Keyboard Always tearin **** Apart??? If nothing else, I get old stuff runnin Before I tear it Down, Just to run Water thru to "Clean" it Out.. Besides...If nothing more than a Numb Nuts adjusted Pushrods Wrong... Some Serious Waste of Time and Effort!!!!
^^ Why, in the Wide World of Sports, is the Folks at the Keyboard Always tearin **** Apart??? If nothing else, I get old stuff runnin Before I tear it Down, Just to run Water thru to "Clean" it Out.. Besides...If nothing more than a Numb Nuts adjusted Pushrods Wrong... Some Serious Waste of Time and Effort!!!!
Some Folks at the Keyboards like to think that the person who is posting a problem does his due diligence to try to resolve it. For me, I look up what was posted previously by them to better understand his issue. We're talking about a 1971 Ironhead here. A top end job on a 53 year old engine is not a bad suggestion. Sorry if you don't like my thoughts on his bike.
Some Folks at the Keyboards like to think that the person who is posting a problem does his due diligence to try to resolve it. For me, I look up what was posted previously by them to better understand his issue. We're talking about a 1971 Ironhead here. A top end job on a 53 year old engine is not a bad suggestion. Sorry if you don't like my thoughts on his bike.
I do Not like tearin **** down that I know Nothing About the History..
I still own a Used Engine that I have Never seen the Inside!! But, I know the Previous Owner, and Some of the History of Work On it..
Runnin just Fine...Friend has a Similar situation...Old Ironhead..Unknown Commodity! We will Do Proper going over, then start it..If No Start...we start with Compression...
If the OP has more info or history on the bike and engine in particular, they should provide it. And sure it's an old Sporty that we know eats valves and guides, but the picture of the plugs from another post didn't look bad in terns of burning oil, although I don't know if they were installed the week before the picture was taken. But if it were mine, I would spend time diagnosing the actual problem befire tearing it down. Including checking pushrod adjustment because that could affect compression. Although that may be what is eventually required.
Agree with Racepres, start with checking the pushrods adjustment. But check and adjust them cold because the cylinder grows taller when they heat up so if you set them hot the valves won't close when cold.
Did you check compression with the engine hot or cold? Did you hold the throttle wide open? The 90 psi isn't too bad, but 30 is bad, surprised you say it runs decent in 1st through 3rd.. If you have a way to put some compressed air in the cylinders one at a time while the valves are closed (remove the pushrods it necessary) and see if the air comes from the intake or exhaust.
Is it smoking out of the exhaust or using oil? Check the spark plugs for lots of carbon buildup (unless they are new). The old iron Sportsters were hard on valve guides, I've seen valve guides bad enough that they allowed oil down the stem so that the back side of the exhaust valve will build up so much carbon it can hold the valve partially open. You could pull the rear exhaust pipe and see how the valve looks. If you do, take a picture(s) and post it.
Agree with Racepres, start with checking the pushrods adjustment. But check and adjust them cold because the cylinder grows taller when they heat up so if you set them hot the valves won't close when cold.
Did you check compression with the engine hot or cold? Did you hold the throttle wide open? The 90 psi isn't too bad, but 30 is bad, surprised you say it runs decent in 1st through 3rd.. If you have a way to put some compressed air in the cylinders one at a time while the valves are closed (remove the pushrods it necessary) and see if the air comes from the intake or exhaust.
Is it smoking out of the exhaust or using oil? Check the spark plugs for lots of carbon buildup (unless they are new). The old iron Sportsters were hard on valve guides, I've seen valve guides bad enough that they allowed oil down the stem so that the back side of the exhaust valve will build up so much carbon it can hold the valve partially open. You could pull the rear exhaust pipe and see how the valve looks. If you do, take a picture(s) and post it.
Paul
just adjusted the pushrods theyre pretty oily for sure when I was doing the compression test I could feel the compression on front cylinder but the rear I couldnt feel nothing just kicking easily and barely got a reading. I can hear it when I kick through the intake pretty easy to kick throhhh but starts up right away and idles and runs through third decent but fourth theres just not enough it losing power. Ill definitely check the other stuff soon thanks!
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No compression
