New chopper, new problem

[CBChop]

Hey all my name is Adam

This is my custom 1984  DOHC cb750 chopper



Custom built frame based on a swedish gooseneck frame
80 spoke wheels
Springer forks
Plus lots more trick bits

The problem I have now is that I can no longer use the standard airbox, so..... I have fitted pods

I know what your going to say, they wont run right, but I have no choice with this one, so I have rejetted the carbs now to a 75 and 110 as described on alot of peoples posts

Then when I took it for her maiden voyage, it would not rev above about 6k, and then started to rattle and knock at top end, so I turned around and headed home, but by the time I got home the knocking was worse and had next to no power.

Has anyone got any ideas of what it could be before I start to strip it down??

If you need any more info please let me know as I need to get it fixed

Thanks in adavance

[shinyribs]

Welcome to the forum.

First off... NICE CHOPPA! Those pipes are perfect! I love it!

I can't be of mush help with the jetting on the CV carbs w/pods. I'm still struggling with that on a bike myself. But it sounds like you have more going on then just jetting issues. It is possible to have run the engine so lean that you hurt it, but I wouldn't go straight to thinking that's your problem just yet.

Always best to start with the basics IMO:


1- If it had power, now it doesn't (which you described) I'd go straight to a compression check.
2- Slack cam chain make a ton of noise
3-Valves out of lash will make a bike run like poo.
4- If the carbs aren't synched properly it'll make all kind of awful rattling and knocking noises.

I'd check compression and go from there. If it's low, then determine whether it is a ring issue or a valve issue.

Put a few drops of oil in the cylinder thru the spark plug hole and recheck the compression. If the numbers rise, you've got a ring issue. If not, it's likely valves. That's not to say there is anything damaged, they may just need adjusting. Good luck with this one. A bike that pretty needs to be back on the road!

[TOOLS1]

Very COOL bike! With all the knocking you describe, could there be an internal engine problem?
TOOLS

[CBChop]

Thanks for the comments guys!

I only ran it up the road and back with standard jets in, then upped the jets and took it for a longer spin,

have taken the rocker cover off to check the valve clearances, and they all seem ok, when turning the engine over by hand there is a certain point in the rotation of the engine when the cam link chain goes slack then tight again.

Im not really the greatest when it comes to engine internals

I suppose the next move is to put the cover back on and do a compression test.

and to top it all off I got a freaking charging problem now too!

[TOOLS1]

You do know that a SOHC engine will bolt right into your frame.
TOOLS

[CBChop]

Will it? I did not know that, I was thinking of an engine swap if things started getting too expensive, as this engine has approx. 70 thousand miles on it

[seestheday]

I'd go with what Shiney and TOOLS said first.

Are you running cheap EMGO pods there, or are those the K&N ones?  Cheap pods can cover one of the air ports on the back of the carbs and make the bike run super lean.

There is a really good thread on dotheton/caferacer about why you shouldn't run cheap pods.

Honda RSC has an instruction manual on how to set up the CV carbs on the CB900F to run velocity stacks on a bored out 900F engine.  If you really need to run pods and get maximum performance I think you'd have to go down that route and do some experimenting with your pods and stock 750 engine.  It requires some significant mods to the carbs though, including completely blocking one of the jets, and making the other one huge.  You'd also end up with what effectively a WOT tuned race bike.  Not ideal for just cruising around town.

If you're cool with a slight performance drop then you should be able to get pods to work.  They do look pretty awesome on your sweet choppa.

[hambone]

cbchop the bike is awesome.this is what I did to get pods to work excellent.revs to redline.pulls all the way to a hundred.surpising power.took me a long time to get it right...here goes...rejet replaced main jets 120s on outer two cylinders #1 #4.used 122.5 main jets on inner two cylinders.75 on primary jets across the board.drilled slide holes (carefully) with# 14.only the existing holes!cut slide springs 1 complete loop.the needle is raised two small washers very small(forget the size I will dig it out if you like).ultra clean carbs and sync of course!now for the pods themselves...I mated all four original airbox boots to the pods.very very important.makes the bike run night and day!!!! I simply cut the flare off the ends inserted aluminum ring so I could clamp rubber to rubber...also inserted aluminum hand made disk in the pod.sort of like a half moon.ive used baffle type too.(one hole in center surrounded by smaller holes)I will try to get pictures up of this...again this is what I did.im at sea level also.alot of elbow grease but inexpensive..alot of trial and error.but well worth it. I sincerely hope this helps.

[hambone]

cbchop I forgot I am at 3 turns out on the air fuel mix srews.