Powerloss uphills at high speed.

I am really getting stumped by my motor's loss of power and ticking at freeway speeds, typically uphill.

I just put in my 2nd JE 10.5 piston. First one cracked. Put my original stock cam back in. Previous Hotcam had 1 extremely worn lobe and rocker.

Bike is just getting broken in at 200mi or so and these original problems are surfacing!! :cheers: Bike has been ridden over 37K miles.

I'm running CA 91 premium. A different CDI, pulse generator, ignition coil, new spark plug (cold), new rockers, and a new timing chain. Temp hasn't exceeded 240 yet, but generally around 215. I verified oil flow to head after re-assembly. D&B Mods with 55/158 jets (i think). Sea level to 1200ft

Bike starts right up and instantly can remove choke. Idles fine and is generally quite powerful. I can blast it from gear to gear to 75 mph quite quickly. However, it pooters out on the freeway after a few minutes and quite certainly uphill at >65 mph speeds. I have to reduce throttle to just below the knocking. I can skirt the knocking a bit by down shifting into 4th, as if I'm lugging the bike in 5th at 70mph?! :ride:

These JE's are hurting my wallet as well as other potential part replacements. My latest thoughts on this may be some valve floating. Do springs commonly wear out after this kind of mileage??? I've noticed one other past threader with the similarly hosed righter-most cam lobe and rocker said his valve seats had turned out to be the culprit. Mine appeared fine when it was apart last.

Feedback is always appreciated. Thanks in advance.

The original CV carb is not the best choice for a performance engine. Load changes (uphill) vacume drops, CV adjusts opening and effects mixture, probably leaning it severely. Better to have a carb that delivers a more controlled mixture with expensive aftermarket parts. Just my personal opinion, others may not agree. I've never had a CV on my bikes but do have similar mods without your problems. The stock cam will aggravate any knocking problem. Valve float would effect all the valves not one. I fail to see how a valve seat would do damage to a cam lobe as well. Cams and rockers usually only fail with a lack of oil but that most often damages all the lobes and rockers. I have heard of Hotcams having failures from soft lobes but I doubt that being valid too. My guess would be an original rocker that had wear being put on the new Hotcam. A 158 main may be too small still.

Edited by valvesrule

I agree... Sounds like a fuel 'lean' condition. Could be several things,float level,fuel supply,overall jetting. Whats the plug look like? Adjust or re-jet until it's black then go back down.

Sounds like you've looked at everything else.

Wouldn't it be nice if it were simply a lean main jet. I believe I have some bigger ones around. I always thought my plugs looked ideal and felt the bike was jetted pretty spot on. I hope I'm wrong. The color level of soot and quantity in my tailpipe indicated appropriate jetting to me as well (a slightly dark grey). The bike has a few holes drilled in the airbox and the exhaust baffle is removed so I wouldn't be terribly surprised if I was running a touch lean.

I'll post my results just after I screw in those jets and ride. Thanks for the responses.

I would try a larger main jet, and make sure that nothing is restricting the flow of fuel. Are you sure that the tank is vented so that it lets air in as fuel is sucked out? Is there a chance you could have a clogged fuel filter?

Put in the larger main jet, then if it's rich in the midrange, drop the metering needle a little bit to compensate.

And I disagree with the comment about the CV carburetor behavior. The big advantage of a CV carburetor is that the fuel flow is supposed to better match the actual air flow. There's no way it's going to go lean when "vacuum drops" if you didn't change altitude as well.

The CV carb will be a REAL pain when the pipe or the air box is opened up at all.

Been 'down that road' many,many,many times.:cheers:

CVs rely on a steady stable airflow. Hence Constant Velocity. A cam and compression change can alter that flow necessitating a change to the diaphrahm spring or port orifice. That's why hod rod engines generally use mechanical not vacuum secondary carbs. If vacuum is reduced or increased at a particular rpm or load it can change how the slide operates. Ther's also a chance this guys problem could be a cdi breaking down when it heats up.

Edited by valvesrule

No, my CDI is good. Had that problem before... I keep a spare now too.

My CV carb has always been real good to me.

Update: Valves were really loose for some reason. Put in a 165 main and 58 S. It absolutely rips now!!! However, I think I'm too rich on the pilot.

I still need to do the long freeway jaunts with the steep grades to fully be sure all is well. I'm both happy and pissed that I had the jets the whole time that might have spared my last piston etc... not to mention all the more power I was missing out on. :ride:

I will update again after more freeway action. :cheers:

Edited by NBelken
stated an incorrect pilot jet size in my test trials

Reminds me of a bike that came into the shop back in the 80s' ,that melted down twice.

Finally he told us that a friend told him, "this is a "high altitude" area and he needed to change the main jet down".:p:lol:

I wonder if he ever took his advice again?:cheers::ride:

Also,He would commute on the freeway everyday 45 miles

Update: I ended up placing another washer under the needle and that seemed to cure all signs of predetonation. I haven't examined plugs yet, and I don't believe jetting is 100% spot on, but as long as I'm not cracking pistons I'm heading in the right direction.

Update: I ended up placing another washer under the needle and that seemed to cure all signs of predetonation. I haven't examined plugs yet, and I don't believe jetting is 100% spot on, but as long as I'm not cracking pistons I'm heading in the right direction.

A quick test is to take a little duct tape to the airbox inlets. If it runs better,it needs a little more jetting.

That's a pretty good tip, hopefully other's will remember that as well.

* My sparkplug looked like I swirled them in dry ovaltine. That's a good thing. 55/165 jetting. I terribly miss the 58S pilot romps with the tremendous acceleration, but it would not idle down normally even with the air screw turned all the way in. Makes me want an aftermarket pipe now to necessitate such a pilot jet.

I have to point out that although being in a fairly chilly 50 degree F ambient air temp, I was barely seeing over 200 deg F dipstick temps after an hour of 40-70 mph romps in the twisties. That seems unreal considering the hi-comp piston action.

The only other concern I have is uncovering the mystery behind the righter-most cam lobe and rocker arm wear. I learned I wasn't the only one to experience this exact phenomenon in my search for the cause. I haven't yet run across anybody else's conclusions to this. :cheers: I don't want to really risk another Hotcam until I know the cause, but I sure do miss the power curve... :ride:

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