1991 evo ! could I have put the cam in wrong ?

backfires through the carb.

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neilw
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1991 evo ! could I have put the cam in wrong ?

#1

Post by neilw »

I had strange noises coming form lower down, I checked the tappets. That involved taking the rocker mounting plate off ,and removing the cam . My last post was regarding how to hold the lifters up.. problem solved thanks to this site , and George's brain storm..
Well I had it all back together and started it up. The tappets had long bled down by then.. it sounded like it was on one cylinder and backfiring through the card. I shut it right off . Then poured a coffee to ponder what was wrong. I re-read Clymer's, and Harley's manuals .
Next I brought the timing line in the inspection hole to the middle of the hole. ( a clue here ,I was pushing the rear wheel in 5th gear with the spark plugs out. ) but when I arrived at the line showing in the hole ,the engine slowly rotated an 1/8 of a turn all by it's self.
Next I noticed only the rear cylinder pushrods could be rotated in that position .
I had the cam out so many times ,and it's possible I got it in and lined up wrong. I certainly learned how to line it up, but that's not saying the final installation was correct .
20 minutes later with another coffee ,I went back out with the intention of removing the cam cover "again" and double checking. This involved removing the gas tank, and I had just removed the outer primary , in the hope the noise was the compensating sprocket but it wasn't . so I put that back on. 16 hours seemed like enough for one day, and I got thinking of all the experience on this forum, so I decided to ask if it is likely anything but a wrong positioned cam...
When I first heard it run so irratic, I thought I better static tune it like I did all my other much older bikes , one 76 shovel, the other's were all pans . I didn't get answers on that ,but did move the plate forward and then backwards . but to no avail. Oh , yeas the pushrods were the same ones i removed and for sure are in the right position.
90 % of this post is just me yapping about nothing of any importance , as usual .
Oh one quick question in the attached photo the module plate as a bunch of marks like on a ruler, I don't see any use for them. Could someone please enlighten me . Oh yeah , I noticed the timing marks on the cam are hard to make out , Onev appears to be lower down ,and another at the top..
2021_0730_011011_007.jpg
2021_0730_011011_007.jpg (86.59 KiB) Viewed 1114 times
IMGP1412 RZ.jpg
IMGP1412 RZ.jpg (102.07 KiB) Viewed 1114 times

Thanks ,Neil
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Re: 1991 evo ! could I have put the cam in wrong ?

#2

Post by RooDog »

Neil....
I expanded your image but couldn't see ant timing marks on any of the three gears, My bad?
I have several suggestions:
1) Get your self a set of adjustable pushrods so you needn't have to disassemble the entire motorcycle just to get inside the cam chest.
2) Lose that plastic breather barrel valve, and get a steel one, The plastic ones are prone to going bad and destroying the bore it runs in.
3) Beware, the Clymer, Haynes, and Chiltonn misinformation filled books, they can lead you astray....
4) The graduation marks on the timing plate are to make it easier to use a strobe to confirm ignition timing.
5) The timing marks on the crank have no relationship with the timing marks in the cam chest.....

If it's really hard to start and backfiring, you probably have the spark "180 out". on the wrong cylinder, or wrong stroke. Do confirm front cylinder TDC.
....RooDog....
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Re: 1991 evo ! could I have put the cam in wrong ?

#3

Post by kitabel »

Cam errors (have nothing to do with ignition):
Cam retarded: very low CCP, weak power, big increase with rpm
Cam advanced: very high CCP, great low speed power, fades with rpm

Many problems are caused by... (wait for it)
not understanding the 4-stroke cycle.
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