Camshafts, Jets, and Other Follies

[a_morti]

So I fitted the CBR400 nc23 camshafts in my CB-1 this afternoon, and the 40/110 jets from the nc23 (up from 35/105).

How does it run? Shitty.

I have to say I'm a bit upset, all in all. It took me three hours just to make it considerably worse.

It ticks over evenly, pulls fine until about 6k or 7k (making an awesome amount of induction noise, is that to be expected?!), then falls flat on its face by 8k. It will get to about 12k if coaxed through with a part throttle, but is WAY down on power.

Am I right in thinking it would need even bigger jets to get it running correctly? This makes little sense to me, since surely it shouldn't need more fuel than CBR, as that must have a bigger airbox and free-er flowing exhaust as standard?

I think I got the camshafts in all correctly. If I had missed a tooth, surely it'd run poorly all through the rev range?

[91cb-1]

As you have already pointed out the cbr will be designed to allow more air into the carbs like wise the exhaust will be designed to be more free flowing, so if you have put the cbr set up onto your bike without changing the air intake or exhaust system you will be smothering the engine. I am not 100% sure what the answer to this issue is but you would have to post all the details of the rest of teh mods you have done. It's like dyno jetting a bike to stage 3 or 4 with out changing the air intake or output it doesn't make sense to do it

[a_morti]

For reference:
Intake: snorkels still on, but internal baffles out. Air filter element changed for universal filter foam element.
Carbs: 40/110 jets from nc23
Engine: camshafts for nc23
Exhaust: no mods (original jap-model stainless system).

I did the airbox mods a while back, and fitted the 110 mains subsequently. It had been running fine apart from a little stumble just before 8k rpm. I had put this down to running lean at the top end of the slow jets, as opening the choke sorted it.

I suppose really I need to find somewhere local with a dyno.

[rigwit]

The CB-1 has longer/larger intake ports/openings, against the cbr 400 derivatives, honda did this to the nc32-engined NC27 to realise more mid range grunt up to top end, and I am sure the standard jetting of NC23 is 35 slow 98 main.........got sent a set of NC 23carbs,instead of proper CB-1,s noticed NC 23 carbs about 1/3rd smaller than NC27.

Can always try to fit NC 23/29 carbs but you'd also need the air box from the model as well might be a way out of it.

[a_morti]

The CB-1 has longer/larger intake ports/openings, against the cbr 400 derivatives, honda did this to the nc32-engined NC27 to realise more mid range grunt up to top end, and I am sure the standard jetting of NC23 is 35 slow 98 main.........got sent a set of NC 23carbs,instead of proper CB-1,s noticed NC 23 carbs about 1/3rd smaller than NC27.

Can always try to fit NC 23/29 carbs but you'd also need the air box from the model as well might be a way out of it.

I think you may be thinking of the Aero? The jets I have came from a Tri-arm.

[rigwit]

All cbr 400rr derivative s use the Keihin VG04carbs........trawling grey import site jets depending on model and designation, the latest cbr 400rr ran 115 mains with 40 slow,so could  get a set of 115's to try,if carbs coming off to do........do the near carb synch, using no2 as base and using feeler blades to get all throttle butterfly's in the ball park see if that helps some.

[ptlcb1]

The CB-1 has longer/larger intake ports/openings, against the cbr 400 derivatives, honda did this to the nc32-engined NC27 to realise more mid range grunt up to top end, and I am sure the standard jetting of NC23 is 35 slow 98 main.........got sent a set of NC 23carbs,instead of proper CB-1,s noticed NC 23 carbs about 1/3rd smaller than NC27.

Can always try to fit NC 23/29 carbs but you'd also need the air box from the model as well might be a way out of it.

I think you may be thinking of the Aero? The jets I have came from a Tri-arm.

I know the US model CB-1s from 1989 and 1990, came from the CB400RR Aero, not the tri-arm.  I think the CB-1s that were produced from 1991 to 1993, had engines from the tri-arm, because the Aero was only produced from 1988 to 1990.

[rigwit]

Try taking out the sub filter element for the carbs  , and try again to see if that helped..........the sub filter and pipework to carbs control the diaphragm and throttle piston (as Honda call it)  negative pressure in the carbs venturi is fed in direct relation to butterfly openings and inducted air this forms a partial vacuum in the chamber and a flow of air through the sub filter to   the inside top of the diaphragm lifting the piston and needle from the main needle/jet metering........if flow is to restrictive fitting a bigger main in might just exaberate  the problem of not lifting enough to overcome the flat spot you say.........2 min fix/try - just have to remove seat fiddle sub filter ,seat back on and road test.

[a_morti]

Try taking out the sub filter element for the carbs  , and try again to see if that helped..........the sub filter and pipework to carbs control the diaphragm and throttle piston (as Honda call it)  negative pressure in the carbs venturi is fed in direct relation to butterfly openings and inducted air this forms a partial vacuum in the chamber and a flow of air through the sub filter to   the inside top of the diaphragm lifting the piston and needle from the main needle/jet metering........if flow is to restrictive fitting a bigger main in might just exaberate  the problem of not lifting enough to overcome the flat spot you say.........2 min fix/try - just have to remove seat fiddle sub filter ,seat back on and road test.

I might be being silly but I really don't follow what you are getting at?

The sub-filter was re-made by me with air filter foam, so it's definitely not blocked and is less restrictive than the original part would have been, even 20 years ago before it disintegrated.

[rigwit]

when i got my CB-1 it didn't have any filter in the sub box, so I used a very course foam infill, if air cannot easily pass from atmospheric pressure through sub filter then this will affect the the operation of the piston slides....bit like breathing through a 1" pipe then trying to breath using a straw.

I noticed in another post, you put the same duel density foam in the sub, take it out and give it a blast see if it makes any difference to your throttle response and overall  output.costs nothing and takes 2 mins to do.

[a_morti]

when i got my CB-1 it didn't have any filter in the sub box, so I used a very course foam infill, if air cannot easily pass from atmospheric pressure through sub filter then this will affect the the operation of the piston slides....bit like breathing through a 1" pipe then trying to breath using a straw.

I noticed in another post, you put the same duel density foam in the sub, take it out and give it a blast see if it makes any difference to your throttle response and overall  output.costs nothing and takes 2 mins to do.

Ah, now I get you. It's a good theory, but remember it was working fine before with that foam in there. The foam is very permeable, btw. It doesn't necessarily look it in that picture but it is, virtually no resistance at all.

[rigwit]

Ah, now I get you. It's a good theory, but remember it was working fine before with that foam in there. The foam is very permeable, btw. It doesn't necessarily look it in that picture but it is, virtually no resistance at all.

Remember you've gone up a size in jets and hit a wall.......if its needing more fuel as you say it will pick up if you gently open the throttle slowly while travelling, without having to try 115,s worth the few mins it takes to remove filter medium and try it nothing to lose.....

[oldsmoker]

a morti,  you are too rich with the 40/110 jets. With the rr cams alone you have more fuel mix coming into the cylinders, but you need to open up the flow through the exhaust to let it out. Add to that the richer mixture and just when the new cams should be kicking in more power your falling flat because there is no place for that extra burnt fuel to go. Think of it as trying to push more water through the same size hose, it just creates backpressure not flow.
  Until you get a freer flowing exhaust you should go back to your previous jets, or MAYBE, just maybe do the 40 slow jet with your old main jet ( I run a 38/110 with two stage foam air filter and removed baffles on stock pipes ). But I think your best bet is the old jet setup for now, leave the cams in though, they should rock!

[a_morti]

I'll be popping in to the local Dyno centre on Wednesday afternoon. Will report back when I know more.

[oldsmoker]

Good move! Looking forward to results