CB 450 project done... need jetting/gearing tips

[Herm21]

I'm running 155's one one of mine, never had a need to go 160 even with the baffles removed and V-stacks. Are you sure it's jetting? Make sure the timing is dead-on, and the carbs are perfectly synced, if one carb is just a little off, at 6k rpm she will bitch a little.

Herm

 

[Hancock]

Thanks Herm, the '74 K7 had 150's in it to start with and near as I can tell I had the timing set perfect and the carbs synced right using visual/feel method of adjusting throttle cables with the idle stops backed off. The bike starts, idles and runs at lower throttle settings perfectly, but it simply will not accelrate cleanly at higher rpm/throttle settings. I did just try a set of 155's and it seemed to help, but still needs a tad more. I guess I can try drilling the 155's to 160 and give it a try.

I am running the wire mesh/cloth tapered pod filters purchased from you, but my home built mufflers are straight through design with the last section drilled with a glass packed can surrounding it (inside looks like an old auto cherry bomb glass pack).

I was just hoping someone else on here had experienced the same issues in regard to jetting requirements with the pods and a very straight through exhaust. If the 160's do not fix it, I will double check my timing (I only static timed...I guess it is "possible" that my advance is not operating correctly, but mechanicaly it looked good) and carb sync.

PS In your opinion Herm, does a 17T/35T gearing combination sound abotu right for 75 mph highway cruising speed?

 

[Hancock]

160's were way too rich and with the gearing change the stock 150's work the best. I checked my static timing and it is dead on the marks (LF mark and F mark) using an aircraft mag timing buzz box. The left side point gap is .012" and the right side gap is .016" (my manual states an allowable gap range between .012 and .016). The advance mechanism is clean and moves smoothly. Spark plugs gapped at .030".

Fifth gear is now basically "overdrive" with the new gearing and is definately more comfortable at 65 mph.

The damn thing is still breaking up a bit when accelerating wide open at about 7500-8000 rpm. I don't know what to check next. It starts, idles and runs perfect until revving over 7500.

I did not install new points, condensor or plugs when I restored the bike as they all seemed servicable. I wonder if any of those items could be the culprit?

 

[Big R]

Points, plugs, and a condensor are all fairly cheap. I would replace them just for peace of mind.

I haven't read the entire thread, but have you replaced the coils with good units? My 175 would break up at high rpm's with a cheap but new coil. Got a Dyna coil and it solved it.

 

[Hancock]

I do have a spare set of coils on a 1972 parts bike..... Maybe I will give them a try.

 

[Hancock]

Installed new plugs, points and condensor..... no change... still breaking up at high rpm.

Found leaking float and changed out with spare from parts bike... no change.

Soldered up then drilled a set of main jets to 140.... Problem solved. I don't get it. This 1974 had 150 mains with stock airbox and mufflers. I can't believe my basically straight thru pipes and emgo KN clones flow LESS air than stock, but this fixed it.

 

[Hancock]

Met my dad halfway at a nearby river town to cruise around on checking out the flood levels. We stopped at a local ice cream shop that was filled with other groups of bikers out enjoying the warm summer evening. We got swarmed by folks riding everything from Harleys to crotch rockets to GoldWings wanting details on Dad's '56 Cushman Eagle and my '74 CB450.

Dad was proud as a peacock as he made sure everyone listening knew his son built both of these bikes.

He put 70 miles on the Cushman earlier in the morning this day. Even though I try to get him to run it harder at 45-50 mph, he still typically cruises at 30. He has put about 1200 miles on it so far

and keeps it waxed and covered. Note the towel under his bag on the luggage rack.... He does not want to scuff the luggage rack paint. He also puts a towel on the floor board temporarily when he kick starts it so the rubber pad on the kickstarter does not scuff the stainless steel floor board.