Topic: 1978 jet needle sets

[drumstyx]

As I was restoring my '78 CB750, I learned a lot, and made many mistakes. One of those included learning that *hard parts in carbs generally don't need replacing*.

At the time, I simply replaced everything in the carb with whatever came in the kits, which at the time came with jet needle sets et al.

Long story short, some deformation of the collars may have led me to mismatching things before I knew any better -- either mismatching old sets with 3 new ones, or possibly even an old collar with a new needle....honestly, just noob mistakes, not great.

I'm going back in to fix a hard start/off-idle throttle response issue with some larger pilot jets (aftermarket exhaust), and I thought I'd have a look at those needle sets while I'm in there, in case that has anything to do with it.

So anyway, I can't seem to find jet needle sets anywhere but CMSNL, or full rebuild kits. I don't really mind if it's OEM or aftermarket, I'd just rather only buy the specific parts I need, I don't need whole sets, and I don't really want to spend 150 Euro if I can avoid it, as they're 31.50 EUR each, plus shipping to Canada...Damn things would be over $220 CAD... Are there keyster sets, or cheaper OEM sets available anywhere?

[drumstyx]

jetsrus has needles if I knew exactly what to look for, but it doesn't look like it comes with the matched collar.

Am I overthinking this? Are collars really tightly matched to the needle? Will a given aftermarket collar perform catastrophically with an OEM needle?

[754]

When you say collar, do you mean the needle seat ?

[drumstyx]

When you say collar, do you mean the needle seat ?

I suppose -- OEM parts sheet has them paired as #3 in the list.

[flybox1]

I have 3 from a set of PD42a's.  One was really stuck and I unfortunately mushroomed it.
Let me know and i'll ship them for a 6-pack.

..or, check with harisuluv to see if he has a full set.

[drumstyx]

I have 3 from a set of PD42a's.  One was really stuck and I unfortunately mushroomed it.
Let me know and i'll ship them for a 6-pack.

..or, check with harisuluv to see if he has a full set.

Do the seats have to be matched to the needle? I mean, I *HAVE* seats, the carbs are together and running, but, I've had issues starting and a hesitation at ~100km/hr whacking it open to accelerate hard. The needles and seats are probably from the (aftermarket) rebuild kits, and I don't recall what original parts I put back in when I realized my mistake of replacing hard parts -- I still have the original needles (as I recall, they're the silver ones, where the aftermarket ones are goldish) and they're *probably* what's in there right now, but I'm thinking all this mis-matching might be causing some issues?

[flybox1]

Its certainly possible, but it could be a number of things....
I dont think the seats have to match the needle, as there shouldnt be an wear where the needle inserts into the needle jet.
Aftermarket parts: the needle taper could be off, the ID of the needle jet could be incorrect....

To your symptoms....Describe for me your cold start procedure.
I spent a crazy amount of time dialing in my accel pump, fast idle cam, and IMS. 
I never had an issue with cold starts after I got it sorted out.  These three have to work in unison.

Remember these are not FI carbs.  'Whacking' it will always make them gasp. 
Try a smooth roll-on from rolling at 60mph/100kph, and see what happens.  make note of the throttle position and how quickly you can reproduce the symptoms.

[drumstyx]

Yeah, I've resolved to be more careful with the throttle, but I want to make it as good as it can be. WOT from about 2500+RPM is fine, except when under load at 80+km/h. If I'm going say, 30km/h, and gun it, it'll pick up like any CV carb.

Cold start....man, this has been a plague. Full choke of course, fuel on and wait until it stops flowing (clear line). If I don't give it a good many accelerator pump squirts (twisting the throttle like a maniac before and during cranking) it won't fire, and usually it'll stall a once or twice before I can get it to stay running.

I'm going in and replacing the accelerator pump, and upping the pilot jets from 35's to 40's because apparently non-stock exhausts actually make a difference on these bikes (and who can afford a stock system??)

With all my learnings, I think I can go back in and make some more educated decisions in tuning.

At that time, I'll be rechecking valve clearance, and timing, all of which are using a great number of brand new components (tappet screws, valves, complete points plate and points OEM).

I never did run a compression test on the newly rebuilt engine, so I guess I should do that too.

[brewsky]

For start up on cold engine, try full choke, couple of quick twists, kill switch to engine-off, and crank it a few seconds first.

Then flip the kill switch on and hit the starter.

My 305 Dream has a separate ignition switch position (crank only/no ignition)  for that purpose.

(It also gets the oil pump operating ahead of the engine being under load)

[flybox1]

Yeah, I've resolved to be more careful with the throttle, but I want to make it as good as it can be. WOT from about 2500+RPM is fine, except when under load at 80+km/h. If I'm going say, 30km/h, and gun it, it'll pick up like any CV carb.

Cold start....man, this has been a plague. Full choke of course, fuel on and wait until it stops flowing (clear line). If I don't give it a good many accelerator pump squirts (twisting the throttle like a maniac before and during cranking) it won't fire, and usually it'll stall a once or twice before I can get it to stay running.  2-3 accel pump squirts and it should light up.  if ^^^this is going on, your fast idle cam and or your IMS are not set right.

I'm going in and replacing the accelerator pump, and upping the pilot jets from 35's to 40's because apparently non-stock exhausts actually make a difference on these bikes (and who can afford a stock system??) 40 pilot jets should have been standard on this model bike.  good choice.

With all my learnings, I think I can go back in and make some more educated decisions in tuning.

At that time, I'll be rechecking valve clearance, and timing, all of which are using a great number of brand new components (tappet screws, valves, complete points plate and points OEM).

I never did run a compression test on the newly rebuilt engine, so I guess I should do that too.

[drumstyx]

Yeah, I've resolved to be more careful with the throttle, but I want to make it as good as it can be. WOT from about 2500+RPM is fine, except when under load at 80+km/h. If I'm going say, 30km/h, and gun it, it'll pick up like any CV carb.

Cold start....man, this has been a plague. Full choke of course, fuel on and wait until it stops flowing (clear line). If I don't give it a good many accelerator pump squirts (twisting the throttle like a maniac before and during cranking) it won't fire, and usually it'll stall a once or twice before I can get it to stay running.  2-3 accel pump squirts and it should light up.  if ^^^this is going on, your fast idle cam and or your IMS are not set right.

I'm going in and replacing the accelerator pump, and upping the pilot jets from 35's to 40's because apparently non-stock exhausts actually make a difference on these bikes (and who can afford a stock system??) 40 pilot jets should have been standard on this model bike.  good choice.

With all my learnings, I think I can go back in and make some more educated decisions in tuning.

At that time, I'll be rechecking valve clearance, and timing, all of which are using a great number of brand new components (tappet screws, valves, complete points plate and points OEM).

I never did run a compression test on the newly rebuilt engine, so I guess I should do that too.

Hmm, so, noting that you say IMS not set correctly could cause what I described, surely bumping the jets 15% larger (35 to 40) will make a pronounced difference. That's good news to me.

It occurs to me that you may be suggesting the fast idle cam opens the throttle TOO much, yes? This'll be an interesting and frustrating fall project I'm sure.

[flybox1]

Put 40 pilot jets in, and turn your IMS to 1 turn out. This should be pretty close...
Once the bike is hot, perform a good idle plug chop, and dial in your IMS so that new/clean plugs come out a light tan after a 5 min idle.

The (FIC)fast idle cam, and idle set screw only do ONE thing....and that is hold slide height to whatever you set them at..
The choke knob adds in the closing of the butterflies to further richen the mixture for starts.
The FIC should lift the slides about 3mm when the choke knob is pulled. The goal is for the FIC to hold your idle at +/-2500rpm....and as the bike warms up, the choke goes off, and the slides fall to where your idle set screw holds idle.
The set screw for the fast idle cam can be turned IN, to increase the slide height(RPM) when you pull the choke for cold starts.