Hawk Carb adventures in 2022

[harpo]

I've had two Hawks over the years, and they both had a throttle hesitation when at constant speed, and at ~ 4,000 rpm. Hesitation (feels like bike is running out of fuel) would be made worse by headwinds or passing a semi. Recently I've noticed the issue can be improved by using the choke when at speed. Therefore I believe the engine is running too lean.

I'm not experienced with motorcycle carbs, only have small engine experience from my go-karting days.

I came across this nice web page for "Carburetor Tuning Guide" http://www.nightrider.com/bt30/carb_jet_ranges.htm For someone line myself, this is great to understand at what throttle openings what variables are at play.

I am going to replace the diaphragms with JBM Industries (Part # K-72-S), and while in there, raise the needle a little to see if it helps the hesitation at midrange. I may also try to back out the Pilot Screw by 1/2 turn.
Carb Tuning Guide.jpg
Plan to update if I get some results and will share pic's.

[Peteroo]

I'd do one thing at a time. Move clip then test ride. Then if it still needs work, go from there otherwise you dont know what went wrong or what helped. You can also kill the power at mid throttle, or wherever theres hesitation, then check plugs. Adjust then retest.

[squirrelman]

no need to replace diaphragms if the bike will reach any speed over about 50 mph. there is also no real need to visually inspect diaphragms as they can be tested by blowing air into the black tubes to see that the slides rise smartly. part of your description seems like a common hawk problem with float bowl vent tubes causing brief loss of power in crosswinds.

you need to get into the carbs and do some basic cleaning and adjusting before planning any carb mods.. your problems might be resolved by cleaning idle jets,opening idle screws a bit or fitting larger idle (pilot) jets.

post-3647-0-85981000-1347898810.jpg

[6]

I'd do one thing at a time. Move clip then test ride. Then if it still needs work, go from there otherwise you dont know what went wrong or what helped. You can also kill the power at mid throttle, or wherever theres hesitation, then check plugs. Adjust then retest.

I agree 100%. Troubleshooting is best done one change at a time. It's a rule I have tried (read "TRIED" Impulse sometimes takes over) to follow racing and somthing I learned in my career in I.T.
The exception being when you have a setup that is way off and you know for sure that there are many things that need to be changed as the start of a project (i.e. full jet kit installation on a bike with an pipe and pods that had stock carbs), or you change a system component that requires other changes (as an example, I'm not against changing spring rate, preload and damping all at once.)

In my expiriance plug chop like that won't show you much at a specific rpm unless the plugs are new. Older plugs will give you a general idea how how the bike is running over all despite what rpm you turn it off last. a black plug won't turn light and chalky with a trip to the stutter rpm. But if it's that lean that much you should be able to see it on the plugs either way.

[harpo]

no need to replace diaphragms if the bike will reach any speed over about 50 mph. there is also no real need to visually inspect diaphragms as they can be tested by blowing air into the black tubes to see that the slides rise smartly. part of your description seems like a common hawk problem with float bowl vent tubes causing brief loss of power in crosswinds.

you need to get into the carbs and do some basic cleaning and adjusting before planning any carb mods.. your problems might be resolved by cleaning idle jets,opening idle screws a bit or fitting larger idle (pilot) jets.

post-3647-0-85981000-1347898810.jpg

After you mentioned the Float Bowl Vent Tubes, and I searched the forum, I was convinced that was the issue. However, I just checked the bike and it seems like the stock vent tubes were kept along with the "sub air cleaner" box. So I'm thinking you are right with the cleaning and inspection of the carbs.


Float Bowl Vent.jpg

[6]

After you mentioned the Float Bowl Vent Tubes, and I searched the forum, I was convinced that was the issue. However, I just checked the bike and it seems like the stock vent tubes were kept along with the "sub air cleaner" box. So I'm thinking you are right with the cleaning and inspection of the carbs.


Float Bowl Vent.jpg

Jerry is a master carb'er... The man knows his way around far better than most.

[harpo]

no need to replace diaphragms if the bike will reach any speed over about 50 mph. there is also no real need to visually inspect diaphragms as they can be tested by blowing air into the black tubes to see that the slides rise smartly. part of your description seems like a common hawk problem with float bowl vent tubes causing brief loss of power in crosswinds.

you need to get into the carbs and do some basic cleaning and adjusting before planning any carb mods.. your problems might be resolved by cleaning idle jets,opening idle screws a bit or fitting larger idle (pilot) jets.

post-3647-0-85981000-1347898810.jpg

You right about the the Pilot Screw! I moved them out 1/2 turn, and the hesitation is completely gone. Just got back from a 60 mile ride, and no issues.

Would you suggest leaving it there, or backing in a 1/4 turn to see if the it can do as well with less?

[squirrelman]

ideally you would follow the service manual idle drop procedure adjusting the screw (on a hot engine) for the fastest rpm at about 1200-1400 idle speed. it needs experimentation in and out to find the best position..

or you could just leave it alone for now since your bike is running better.

[harpo]

ideally you would follow the service manual idle drop procedure adjusting the screw (on a hot engine) for the fastest rpm at about 1200-1400 idle speed. it needs experimentation in and out to find the best position..

or you could just leave it alone for now since your bike is running better.

I'm tempted to leave it alone for now. I can't tell you what a difference it made. At the same point where the bike used to almost cut out, it now pulls strong, SO much more enjoyable to ride.

Thanks sharing your thoughts on this!