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Discussion Starter · #1 · (Edited)
I am still making progress on this bike but I have
some questions.
#1 The throttle is stiff and hard to twist.
New cable did not help. The throttle snaps back
strong but is hard to twist, the springs on the carbs are
strong, is this normal???
#2 I replaced the power chamber/collector box or whatever
you want to call it. How hot does that thing get??? Is 1200f
paint good enough for it?? anyone have decent heat shields for
that box??? I know, a lot of guys dump the collector box and
air box but I want to avoid unnecessary problems.
#3 Still looking for a seat and tail light. I think I may re-cover
the seat and go with that for now.
#4 I am rebuilding the brake caliper, what grease should I
use for the sliders and boots???
Got to pull the carbs again, left side overflowing and running
on the right side only. This thing will run and be ridden soon,
I do not quit when I can see the light at the end of the tunnel.
I guess running on 1 cylinder is some light???
 

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#1. The throttle return springs on the VB21 carbs are stiffer than the 22's. There's a significant difference between my bikes with each version.
#2 & #3. no help there
#4. I use waterproof bearing grease on the caliper slides
 

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Discussion Starter · #3 ·
Would white lithium grease work, said to be waterproof???
I do not want to use greae that will attack the rubber boots.
I can't find anything wrong with the throttle, just very hard to twist.
 

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Discussion Starter · #5 · (Edited)
Still running on right cylinder only and I am about out of ideas.
Pulled the carbs and worked on the float and float valve and the carb seems OK now.
The bike started on both cylinders and ran for about 3 minutes and went back to one again.
Seems like the left side quits after it gets warmed up a little. I thought it was fuel so I made
a small port in the in the intake boot at the air box and injected starting fluid into the cylinder
and it made no difference. I wonder if a sticky valve could cause this problem. It ran ok until
it warmed up. While the left side was not firing there is plenty of spark and there are some small
popping sounds at times. I will try again tomorrow when the engine is cold, first a compression check,
then start and see what it does. If the left side does not run when warmed up I will try a compression check
on the warm engine. I tried 2 different spark plugs and also did the brass rod mod to the plug cap, no help,
nothing changed. I had several Briggs and Stratton engines come into my shop with stuck valves caused by
burning stale fuel with ethanol in it. I think I may pull the valve cover and see what is there. Probably need to
adjust the valves any way. All help/ideas appreciated.

Edit: Bike has 150 psi on both cylinders, started on both cylinders today, ran about 1 minute and lost the left side, as usual. Left side will come in at higher rpm's. Still could be low speed circuit of carb.
Pulling the carbs again to see what I can find. Will check to see if partial choke helps???
 

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Discussion Starter · #7 ·
I think D8EA. I have done everything I know to do and I still have a single cylinder bike.
One thing strange is that it will run OK after it sets for a day. It will start OK and run for
a minute and then drop the left cylinder. I have been working with the idea that it is fuel starvation
but I am going to change and try working as if the cylinder is running rich. Starts instantly every time,
FWIW. I see in the official green manual that the emulsion tubes can not be removed, is that true??
I have removed the tubes several times on VB25A carbs, CX500. I usually find the emulsion tubes are
very clogged and need cleaning. I will change my approach to this bike and see if that does any good.
I really like the sound of this bike when it runs. Seems to be light weight and powerful.
 

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Yeah, the slow/idle jet is a pressed in unit. I've successfully removed them @50% of the time using a high quality easy out/screw extractor. They tend to be frozen in place, heat has seemed to help. I've used a heated ultra sonic cleaner unit to get the carb body really hot, @1 hour of run time, before attempting. Even the emulsion tube under the primary main is a booger to get out and it's threaded, the small brass ears of the slot tend to tear off. I've ground a couple of screwdrivers so the blade has parallel faces instead of tapered and that seems to help plus they just barely fit the bore
 

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Discussion Starter · #9 ·
And the next chapter...........Had the carbs off today and did everything I knew to do and
she till runs mostly on the right cylinder. I did make a discovery though, I have a little electronic tachometer.
Since my tach cable is broken I used the electronic tach to set the idle.....The left side, the non running side,
would show vastly different rpm than the right side. Right side 2700, left side 600, 800, 1000, flopping around
but never equal to the right side. I use this little tach to check lawn mower engines and it is pretty accurate.
The carbs were out of synch but I can handle that, when the thing runs on both cylinders. The difference in
rpm makes me think ignition. Now what??? CDI, coil, stator???
 

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This is a wasted spark ignition system meaning the both plugs are firing at the same time. Plug wires can be swapped side to side without affecting anything. If the coil is firing then it's sending voltage through both wires or at least trying to. What is the secondary resistance, tested w/o the plug end caps? What's the resistance of the plug end caps? Is this an original coil?
 

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Discussion Starter · #11 ·
That was my question, can half a coil fail??? So the problem must be in the spark plug wire???
Yes, original coil, I have not tested the coil yet, got disgusted and quit for the day.
Funny thing, I kept hearing a clicking sound and thought it was a tappet,
probably a leaking spark plug wire. Will try again tomorrow.
I even planned to run the engine in the dark so I could look for sparks where there should not be sparks.
I substituted a brass rod for the resistor in the plug cap and that made no difference.
I will do some testing tomorrow. This thing is gonna run, my grandson asks me everyday, is it running????
 

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Discussion Starter · #12 ·
Can someone point me to that GM coil mod??? Please
 

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Discussion Starter · #14 ·
Another chapter.....today I clipped the end of the spark plug wire back to fresh copper wire and put the plug
cap back on, she ran just fine, both cylinders for about 2 minutes and then went back to mostly right cylinder.
I checked the coil and wiring for breaks or damage and found none. After a few minutes and the engine fully warmed up
she stuttered and died and will not start. Do I need a new coil???

Some test results, HF MM with new battery, meter shows no residual resistance.

Coil primary 1.3
Coil secondary No reading at all
Bl/Wh 92
Pink/Green 143
Br/Lt Bl 229
Did not test for charging. To test coil secondary I put a probe into the open ends of the
spark plug wires?????
 

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Not sure how accurate the HF VOM is going to be but realistically it should be fairly close. By your readings you need a coil and a stator, everything is way out of spec. You did test the secondary side correctly, one probe into each end of the plug wire w/o the plug end caps.
I kind of surprised you got it to start and run.
 

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Discussion Starter · #16 ·
It always started easy if you wanted a one cylinder bike. I may do the GM coil deal but
I am not sure how big the unit is or if there is really room for it under the tank. I like the
idea of having replaceable plug wires. How hard is it to change the stator and pickup??
On my CX500 it is engine out to replace stator. This CB has been a pain to get it running
but we will succeed. I picked up a 1978 CX500 several years ago, not running. I was advised that
cleaning the carbs would make it run. Cleaned the carbs 3 times, finally replaced the CDI
and it has ran ever since.
 

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The coil doesn't fit under the tank, it's too tall. Closeup and distance shot give you an idea of what it looks like.
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Replacing the stator isn't a big deal, you need a 20mm x 1.5 pitch bolt to remove the rotor, 3 Philips head screws hold the stator and 2 more for the timing pickup
 
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