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Throttle Response Problem

Dr. Frankenstein
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Posts: 559
Joined: Tue Feb 02, 2010 7:11 pm
Location: Charlottesville, VA

Throttle Response Problem

Post by Dr. Frankenstein » Wed Apr 24, 2019 4:10 pm

OK, settle in this may take a bit: I was trying to tune the CA77/PW22 carb, and took the bike out for a quick run up and down the road; when in gear and underway, I roll on the throttle and get Minimal response, and grudgingly at that - the bike does not want to accelerate at all, and seems to choke, like there's a dead spot in the carb.

Now, when it's sitting idling, I get GREAT response from the throttle, but hop on and twist it in gear, Nope, not so much.

I noticed that my clutch is pretty tight, i.e. there's not much room between pulling the clutch in and letting it out; and the more I think about it, it might be a clutch adjustment problem, but I thought I would ask here and get a second opinion.

Interesting Tidbit #2: Yes, I did take apart the carb - again - and go through it thoroughly. All my passages are clear, I have the floats set to 26.5mm from the carb body, I do have positive fuel flow through it - and as an aside question, the little cutout in the little bakelite carb mounting plate goes Down, yes...? So it mates up with the cutout in the carb throat...? I'm just checking...

So it's Not the carb, or at least I don't believe so - but what would make it idle and rev Great, but then not accelerate at all? Like I said, I Did notice that when I pulled the clutch in, it seemed to not want to disengage unless I really Pulled it in, but then it was fine - could I have the clutch too tight?

But even if that was the problem, I should still be able to accelerate...FYI, the pilot jet is 35, the Main jet is 120, and the needle seat is 20, and pristinely clean...

Any ideas...?

rrietman
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Joined: Mon Oct 13, 2008 6:45 pm
Location: bellingham wa.

Post by rrietman » Wed Apr 24, 2019 10:21 pm

are you sure you are firing on both cylinders? your symptoms sound like a dead cylinder. plug wire or bad /fouled plug. trim the wire back 1/4" and make sure the cap contacts are clean.
Good luck
Randy

Dr. Frankenstein
honda305.com Member
Posts: 559
Joined: Tue Feb 02, 2010 7:11 pm
Location: Charlottesville, VA

Post by Dr. Frankenstein » Thu Apr 25, 2019 4:07 am

It seems to be firing on both cylinders, but I'll check - I'll make sure I have spark, etc; it Has been a while since the build started.

But why will it rev Great when it's standing still, but under load it dogs out? I get a nice output from both exhausts, but when I put it in gear and try to accelerate, it doesn't. Why is that? The carb is working fine, and I *believe I have spark on both cylinders - but I'll check that - something somewhere is not going Bang when it should.

Geoff Hastings
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Location: Epsom, Surrey

Post by Geoff Hastings » Thu Apr 25, 2019 7:20 am

Easy way to check if it's firing on both cylinders when under load, put a different finger on each exhaust header, The finger without a blister shows that cylinder is not firing. The cutout on the insulator does go to the bottom, Did you notice it also has a small hole in the metal insert, is this clear. I don't think it's a clutch problem, if it was severely slipping you'd get more revs not less.

Dr. Frankenstein
honda305.com Member
Posts: 559
Joined: Tue Feb 02, 2010 7:11 pm
Location: Charlottesville, VA

Post by Dr. Frankenstein » Thu Apr 25, 2019 7:32 am

"..put a different finger on each exhaust header, The finger without a blister shows that cylinder is not firing."

Ah - Humor. ;)

I think I'll try trimming the wire first.


Yeah, I don't think it's a clutch problem either, but I'm stumped as to what kind of fuel problem it could be...the carb is very clean; the throttle valve moves easily in it's cylinder; it revs great when just sitting there; the throttle itself moves great-but put it in gear and put it on the road and it just dogs out...

Geoff Hastings
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Posts: 235
Joined: Wed Feb 22, 2017 2:59 pm
Location: Epsom, Surrey

Post by Geoff Hastings » Thu Apr 25, 2019 10:13 am

The symptoms still sound like a carb problem but if you cleaned all the jets and all the passages and have the float height correct and have checked the carb flange for flatness ( they bend easy) then I'd suspect a HT problem, or even a dodgy plug. I fitted new plugs on my CA77 and one kept fouling up, fitted another new plug and has been fine ever since. I also cut both HT leads off the coil and soldered new leads as close to the coil as I could just to eliminate them.

Dr. Frankenstein
honda305.com Member
Posts: 559
Joined: Tue Feb 02, 2010 7:11 pm
Location: Charlottesville, VA

Post by Dr. Frankenstein » Thu Apr 25, 2019 4:18 pm

Maybe - but the flanges tighten down really well - I wonder if I need a new carb o-ring/s...I still have yet to try trimming the spark wires, though...

See "My No-Fuel Mystery"...

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