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84 Evo loses power under load

M

Matt Bradley

Member
Hey all, hoping someone can offer me some advice because I'm all out of ideas. Bought an 84 FLTC with the evo last fall from someone as a project. Bike was not running when I purchased it. Guy who had it was not mechanically inclined at all. He tried to change the bars and crossed some wires. I fixed the wiring and bike fired right up. He told me the motor had been built up by the guy he got it from but he didn't have any paperwork for it and didn't know exactly what it had. The rear base gasket was leaking so bad it was blowing oil bubbles and it was almost impossible to shift so I figured it'd be my winter project. I put about 200 miles on it before the snow came and it ran decent. So I pull the engine all apart. The motor does have high compression pistons, double valve springs, and ported and polished heads. I do not know the displacement or compression ratio. All the info on the end of the cam was ground off so I have no idea what cam was in it so I ordered an EV27 to replace it. I put it all back together with new gaskets. Set the jets at 48/195. The ignition timing gave me a very hard time. Set it with the bike warm at 2000 rpm so it would be at full advance. I checked the VOES. The cam plate is turned almost all the way clockwise (retard I believe) but I got the timing mark centered in the inspection hole. Go to take it for a test ride. Bike runs awesome at idle to 1/4 throttle under a light load but as soon as you crack the throttle, the exhaust pitch completely changes and it loses all power. It doesn't back fire or sputter. It just does nothing besides get louder and slowly gain speed. I thought the jetting was off so I tried everything from 45-50 pilot and 185-205 main and it still does the same thing no matter what. Has new plugs, wires, and coil. Do I need and aftermarket ignition with an adjustable timing advance? Could I have a bad ignition module? I am 100% sure the cam timing is correct I just don't know where to go from here.
 
Sounds like a timing issue, when under load it may not be advancing like it should.
In your post you said it ran decent before you tore it apart so i'd be looking at how it went back together.
 
Ok thanks. I never marked the cam plate before I pulled it off and when I went to put it back together there were marks in a couple different places like someone had issue with the timing before. I guess I'll put it back on the stand and verify it's right this weekend. Is 2000 rpms an acceptable engine speed for setting the timimg? I've read several posts and saw people saying anything from 1000 rpms - 2500 rpms.
 
Matt Bradley said:
Ok thanks. I never marked the cam plate before I pulled it off and when I went to put it back together there were marks in a couple different places like someone had issue with the timing before. I guess I'll put it back on the stand and verify it's right this weekend. Is 2000 rpms an acceptable engine speed for setting the timimg? I've read several posts and saw people saying anything from 1000 rpms - 2500 rpms.
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How many miles on the clutch system? Maybe it's slipping under a load?
 
It doesn't feel like the clutch. It's doesn't rev out and not go anywhere. It barely builds and rpm. I had the clutch apart to clean it and install a clutch tamer and everything looked good when I was in there. Pressure plate is set at 31/32".
 
It may be a gross air leak in the intake tract. Check everything from the carb. mount to the intake flanges at the heads. I set my electronic ign. with the engine off. Mark in the middle of hole (how many marks are on your flywheel? some have adv. and tdc marks), and rotate the plate until spark happens. I use a radio next to the bike, set on AM, tuned to static between stations. When spark happens, "POP" is heard on radio. Then the VOES takes care of the advance when running. I ASSume you are running a Keihn butterfly carb?
 
No it has a later model CV carb on it. I did change the intake gaskets but I'll check them and make sure they're not leaking. I have the 1 line on the flywheel for TDC and the single dot for 35* BTDC. I set the mark to the center of the inspection hole at 2000 rpms but maybe I'll try the AM radio trick.
 
Also check the fuel filter and that the shut off valve allows full fuel flow.
Starving for fuel can cause the same symptoms.
 
OK, I wasn't thinking CV carb. There may be a problem with the diaphragm in the carb, and the slide is not getting the vac. needed to rise out of the air flow, and allow the engine to rev. That fits your symptoms well. IMO Look into the carb. throat while running and see if the slide responds with rpm increase.
 
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