Jetting Question

[Mr. Philadelphia]

I last owned a Hawk in 1997 but just finished up with a frame up build on what will eventually be the last bike I ride. All the characteristics that made the Hawk a perfect track bike, 1st bike, and light weight canyon carver also make it the perfect old man's bike. I reckon I'll still be ripping around on this thing when I'm 80.

I any case, I just wanted to post some jetting questions.

Runs Great Across the range with this setup:

4" UNI Pod Filters
Two Brothers full system exhaust from the 90s
Factory Pro Stage 3 needles set on the 3rd Slot
New Float Seats & Valves
42 Pilot Jet
The bike would bog down at 7K rpm in 4th & 5th gear, then pick back up after rpms dropped back down to 6K.

I thought the main jets might be too rich so I dropped down to 165 F, 162 R.
This setup was too lean, especially below 3-4K rpm with popping in the exhaust and an occasional backfire through the front carb. Things improved at wider throttle openings when the slides began to lift. I tried turning out the pilot screws some more, but it still ran like crap. And the idle behaved like it was running too rich as after blipping the throttle, the tach would dip below idle and then climb back up to normal. With these main jets, the idle was actually better with the pilot screws 1 turn out.

Question: Why would swapping out the main jets cause such terrible fueling in the lower rpm range?

The carbs were a mess when I first opened them up. After pulling them off 5-6 times during this experimentation process, I decided to pull out the float valve seats and found more sediment in the front carb. I think this caused the bogging at WOT in 4th and 5th gear (fuel starvation), though I haven't had a chance to test it.

IMG_2686-800x600.jpg IMG_2687-800x600.jpg IMG_2689-800x600.jpg IMG_2814-800x600.jpg

[squirrelman]

wow, you started with some really filthy carbs gonna need an ultrasonic cleaner for dem bitches for sure.

dija carb spray and blast air into the idle mixture screw hole ? with stock idle jets, mixture screw should be two to two point 5. optimize screw setting according to the "idle drop" procedure in the manual. float height set correctly=nine mm ? maybe the slide needle needs adjustment for your setup; if lean, raise it one notch.

main jets MUST be selected FIRST for maximum top speed, around one hundred fifteen mph [on my bike].

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[Mr. Philadelphia]

IMG_2814.jpg Thanks for your input. I set the idle according to the manual, and the floats sit at 9.1mm. I've cleaned & blown out the all the fuel and air orifices several times thinking that might be the problem, but why going down on the main jets a few sizes would affect low throttle/rpm running befuddles me.

[squirrelman]

study the curves that parknhawk posts to see how the rev ranges overlap and interact

[Mr. Philadelphia]

That's a great chart. Thanks. But I'm wondering if there might be some other dynamics going on with my carbs in particular. Main jets should have minimal effect from start of throttle opening to 3/4 opening. But for whatever reason, my bike ran lean on the smaller main jets from closed to 1/4 throttle opening. Maybe there was some stubborn debris in the pilot circuit that dislodged when I blew things out the last time I had the carbs off, but I started with the larger main jets & settings from my 1st post and it ran fine except for WOT in 4th & 5th gears at 7K rpm, which I've since attributed to a fuel supply issue. When I put in the165/162 mains it seamed to run lean in general, but worst from beginning of throttle opening to around 1/4. Nothing improved in the low range after having removed the carbs 3-4 times to clean and recheck float levels until I put the 170/165 jets back in there the last time. It always idled just fine but ran lean, stumbling and popping from start of throttle opening to around 1/4 opening.

wow, you started with some really filthy carbs gonna need an ultrasonic cleaner for dem bitches for sure.

Not the worst I've seen, but oh man, RTV all over inside & out. I hope the owner who did this is not a member here, but RTV instead of proper float bowl gaskets ???!!! C'MON, man! The clutch pack was missing the last disc B that caused slipping at WOT in 4th & 5th gears, which I initially thought was a fueling problem. Fixed the clutch only to realize that I had a fueling problem as well. I rebuilt the vacuum pump and replaced the float valves & seats so I think I'm all set at this point, but still at a quandary regarding the main jet changes.

[Hordpower]

>Question: Why would swapping out the main jets cause such terrible fueling in the lower rpm range?<

They wouldn't. You have something else going on.

[Mr. Philadelphia]

Word, so I'm not crazy. It's running great now so I'll update down the road when I feel like pulling the carbs and experimenting with the mains again.

[6]

The answer to 99% of carburetor questions on the forum.

"Clean them again."

Haha.

Glad you have it going!!

[Mr. Philadelphia]

The answer to 99% of carburetor questions on the forum.

"Clean them again."

Haha.

No joke.

20 miles into my Sunday morning ride up to the mountains I suffered the same symptoms of power loss at WOT & 7K rpm in 5th gear so I turned around & decided on another Sunday carb day instead -- went through it all over again disassembling everything except for separating the carbs. I focused on cleaning out the pilot jet circuit ... again ... so much aluminum corrosion on these carbs that must get kicked loose with use. I worked a small diameter stainless wire through the 4 pilot orifices in the venturi, sprayed & blew out everything ... again & again ...

Here's what I think was happening, I was running rich all throughout the range except for the pilot circuit, which would intermittently get clogged up probably at the orifices in the venturi. This lean running would heat things up during slow speed operation in the city so that when the rich mixture came at wider throttle openings, I'd get some backfiring through the exhaust & a couple of times through the front carb.

Moved the clip up from the 3rd to the 4th position & switched again to 165 front/162 rear mains (from 170F/165R). Took it for a ride and all seems well but still need to check WOT in 5th gear early one morning. But at least now, I can start dialing in the mains without thinking I'm crazy.

[6]

I had a bike with an iffy tank. The rust sediment would work it's way through the filters, build up in the bowls and eventually clog a circuit.

If you have corroded carb bodies you may be dealing with a similar but different issue. Have you done a full cleaning of the bodies in either a chemical dip or ultrasonic? That may be the next step if this keeps up.

[Mr. Philadelphia]

I did the Caswell epoxy coating inside the tank and still have a little bit of rust sediment working it's way out. I've found the Hawk tank one of the most difficult to fully drain -- always a last little bit that sloshes around inside.

I did put the carbs in an ultrasonic cleaner when I had them separated but probably should have left them in there longer. Hopefully manually cleaning the pilot orifices in the venturi did the trick. I'll let you know it goes as I try to dial in the mains.

[6]

I did the Caswell epoxy coating inside the tank and still have a little bit of rust sediment working it's way out. I've found the Hawk tank one of the most difficult to fully drain -- always a last little bit that sloshes around inside.

I did put the carbs in an ultrasonic cleaner when I had them separated but probably should have left them in there longer. Hopefully manually cleaning the pilot orifices in the venturi did the trick. I'll let you know it goes as I try to dial in the mains.

Nice. Fingers crossed for you man.

[Forcerouge]

I did the Caswell epoxy coating inside the tank and still have a little bit of rust sediment working it's way out. I've found the Hawk tank one of the most difficult to fully drain -- always a last little bit that sloshes around inside..

Yeah you need some kind of pump to get everything out.
Getting everything outside of it just by shaking is close to impossible.

If you are curious to see how it is made inside, you can have a look at these pics I took while cutting my tank in half: https://www.hawkgtforum.com/forum/ho...431#post969431

It helps a lot to understand why this is such a nightmare

[Ziggy]

Something that I found to aid draining the tank is to use a small cut off wheel and shorten the sleeve that extends into the tank at the fuel filler opening.
The sleeve can be shortened approx 1/4" up to the bottom of the pocket for the filler cap. Use caution not to cut into the pocket.
The sleeve I am referring to is not at the bottom of the pocket but behind it inside the tank.
This modification does not completely address the draining issue but helps.
Look at the pictures in the above link of the tank that Forcerouge posted to view the sleeve I am referring to.

[Henway]

I use my Mighty-vac brake bleeder with a 24" tube and stand the tank up and put the tube so it's at the bottom. I think I pull out more than 500ml of gas after nothing comes out on reserve any more.