Author Topic: false air CB750 F2 (Read 3540 times)

koendd · « **on:** October 28, 2015, 12:55:14 PM »

So,

I'm having this anoying issue with my F2...

since I've rebuild the head I can't get the idle right on my bike. When it's idling and give it a rev, it keeps on going at around 3-4k RPM.

so it's getting air somewhere.... I've mounted new intake boots, but it's still doing it...
Is it possible air is getting in through were the carbs boots are mounted on the head?

if so, what O-rings do you need, and where do you get them? I can't find them listed anywhere...

If not, what else might cause this problem?

flybox1 · « **Reply #1 on:** October 28, 2015, 01:19:57 PM »

no orings on the intakes like the 550's.
first place to look is, yes, air leaks on the boots to the head.
id remove the carbs and complete a more accurate bench sync, and then attempt idle again.
a vacuum sync will really help to get it settled down.

koendd · « **Reply #2 on:** October 28, 2015, 02:11:04 PM »

Quote from: flybox1 on October 28, 2015, 01:19:57 PM

no orings on the intakes like the 550's.
first place to look is, yes, air leaks on the boots to the head.
id remove the carbs and complete a more accurate bench sync, and then attempt idle again.
a vacuum sync will really help to get it settled down.

well boots and clamps are new, and did a Vac sync just yesterday..

guess I'll pull them again and see if I can do something else with the carbs :p

flybox1 · « **Reply #3 on:** October 28, 2015, 02:22:34 PM »

Set your #1,3,4 vac sync screws (under the top caps) so they have the same # of threads showing above the lock nut.
Bench sync heights to match #2 and check that your slides completely close when you turn your idle set screw all the way out.

koendd · « **Reply #4 on:** October 28, 2015, 02:37:51 PM »

Quote from: flybox1 on October 28, 2015, 02:22:34 PM

Set your #1,3,4 vac sync screws (under the top caps) so they have the same # of threads showing above the lock nut.
Bench sync heights to match #2 and check that your slides completely close when you turn your idle set screw all the way out.

allright! thx for the info!

reads someone was having an airleak between intake ports and head. Could it be worth taking them off and put some sealant on it or is it a real small chance it's coming from there?

Cause I can clearly hear a RPM chance when spraying carb cleaner there...

flybox1 · « **Reply #5 on:** October 28, 2015, 02:44:31 PM »

Quote from: koendd on October 28, 2015, 02:37:51 PM

Cause I can clearly hear a RPM chance when spraying carb cleaner there...

fix this first!

koendd · « **Reply #6 on:** October 28, 2015, 02:57:14 PM »

Quote from: flybox1 on October 28, 2015, 02:44:31 PM

Quote from: koendd on October 28, 2015, 02:37:51 PM
Cause I can clearly hear a RPM chance when spraying carb cleaner there...
fix this first!

that's what I plan on doing, hence my question, is it worth removing intake ports and putting some sealent on it?

madmtnmotors · « **Reply #7 on:** October 28, 2015, 05:49:37 PM »

Quote from: koendd on October 28, 2015, 12:55:14 PM

so it's getting air somewhere.... I've mounted new intake boots, but it's still doing it...

New boots between the air cleaner and carbs, or new boots between the carbs and head? Did you buy new band clamps too?

Quote from: koendd on October 28, 2015, 12:55:14 PM

Is it possible air is getting in through were the carbs boots are mounted on the head?

Are you talking about between the aluminum intake spigots and the head itself? If so, then absolutely not. If you have a leak here then you have bigger problems...

Don R · « **Reply #8 on:** October 28, 2015, 07:57:22 PM »

You would likely destroy the aluminum nipples trying to remove them. They are not meant to unscrew.
The guys above described it better than I did on facebook, listen to them.

koendd · « **Reply #9 on:** October 28, 2015, 11:06:53 PM »

Quote from: madmtnmotors on October 28, 2015, 05:49:37 PM

Quote from: koendd on October 28, 2015, 12:55:14 PM
so it's getting air somewhere.... I've mounted new intake boots, but it's still doing it...

New boots between the air cleaner and carbs, or new boots between the carbs and head? Did you buy new band clamps too?

Quote from: koendd on October 28, 2015, 12:55:14 PM
Is it possible air is getting in through were the carbs boots are mounted on the head?

Are you talking about between the aluminum intake spigots and the head itself? If so, then absolutely not. If you have a leak here then you have bigger problems...

boots between head and carbs are new, as are the clamps...

and ok, you saved me a lot of time and broken parts by asking first then about the instake spigots

koendd · « **Reply #10 on:** October 30, 2015, 07:18:21 AM »

went throught the 3000mile service yesterday and this morning.
so checked timing, adjusted the valve clearence to spec, took the carbs off cleaned everything and put them back on and he still does it!

no more change in rpm when I spray brake cleaner though...

I did chance the gas needles about 1000km after the rebuild this summer because it was running a bit lean. so I changed the clip to one notch down from stock. (stock airbox, open 4/1 exhaust)

can this be the problem?

flybox1 · « **Reply #11 on:** October 30, 2015, 07:28:08 AM »

Quote from: koendd on October 30, 2015, 07:18:21 AM

went throught the 3000mile service yesterday and this morning.
so checked timing, adjusted the valve clearence to spec, took the carbs off cleaned everything and put them back on and he still does it!

no more change in rpm when I spray brake cleaner though...

I did chance the gas needles about 1000km after the rebuild this summer because it was running a bit lean. so I changed the clip to one notch down from stock. (stock airbox, open 4/1 exhaust)

can this be the problem?

How did you determine it was running lean and needed a NEEDLE CLIP change?
seems like an odd change for your airbox and exhaust $:-\$

koendd · « **Reply #12 on:** October 30, 2015, 08:00:15 AM »

Quote from: flybox1 on October 30, 2015, 07:28:08 AM

Quote from: koendd on October 30, 2015, 07:18:21 AM
went throught the 3000mile service yesterday and this morning.
so checked timing, adjusted the valve clearence to spec, took the carbs off cleaned everything and put them back on and he still does it!

no more change in rpm when I spray brake cleaner though...

I did chance the gas needles about 1000km after the rebuild this summer because it was running a bit lean. so I changed the clip to one notch down from stock. (stock airbox, open 4/1 exhaust)

can this be the problem?
How did you determine it was running lean and needed a NEEDLE CLIP change?
seems like an odd change for your airbox and exhaust $:-\$

popping in the exhaust and white plugs..
Started searching here on the forum and found that might do the trick...

guess it didn't help much (not running lean now though)

also disconnected the cables to rule them out. And did throttle by hand. Didn't do it as much but still sometimes... after I gave it another rev when it was 'stuck' it almost always drops down to idle like normal.

could it be a needle sticking or something.

flybox1 · « **Reply #13 on:** October 30, 2015, 08:16:03 AM »

yes, popping and white plugs are a sign of lean-ness, but what throttle position are you talking about?
2/3 throttle position? if so, then yes, needle clip change here will richen this throttle position.
If your popping and white plugs was at idle, or low speed, then you've adjusted the wrong part of your carbs.

you need to tell us the conditions in which you had popping and white plugs.

koendd · « **Reply #14 on:** October 30, 2015, 08:23:24 AM »

Quote from: flybox1 on October 30, 2015, 08:16:03 AM

yes, popping and white plugs are a sign of lean-ness, but what throttle position are you talking about?
2/3 throttle position? if so, then yes, needle clip change here will richen this throttle position.
If your popping and white plugs was at idle, or low speed, then you've adjusted the wrong part of your carbs.

you need to tell us the conditions in which you had popping and white plugs.

at idle when releasing the throttle.

like when you are riding at higher speeds and need to stop, it would pop quite a bit when releasing the throttle

flybox1 · « **Reply #15 on:** October 30, 2015, 08:25:01 AM »

yeah...you've adjusted the wrong part of your carbs.

Quite a few parts of your carbs contribute to a proper air/fuel mixture, and the primary fuel contributor depends on what throttle position you are in.
check out the chart below.
if youre riding all the time in 1/4 throttle position, and you get your popping and white plugs, then look at the chart. adjust the primary fuel contributor at 1/4 throttle....which is going to be your pilot jet and mixture screw.

Put your needle clips back to where they should be, and make the correct changes

flybox1 · « **Reply #16 on:** October 30, 2015, 08:28:48 AM »

Incorrect mixture at:
WOT - Adjust your main jet
2/3 throttle - adjust your needle clip position
1/4 throttle - adjust your pilot jet
idle - adjust your mixture screw

Because of the overlap in the above chart, your mixture tuning needs to be done in the order listed above.
As I suggested, get your clips back to where they were. Turn your mixture screws RICHER one full turn.
This might be enough to allow you to idle well and vacuum sync your carbs.
See how it runs and check plug color.
If they're still white, you'll need to go up a size in pilot jet, and turn your mixture screws back leaner one full turn.

koendd · « **Reply #17 on:** October 30, 2015, 08:29:06 AM »

okay, thx!

allready put a 110main in yesterday (105 stock). So that would be a better solution?

flybox1 · « **Reply #18 on:** October 30, 2015, 08:37:22 AM »

You are LEAN AT IDLE. Why are you making wide open throttle (main jet) richer?

you totally missed the purpose of the chart

read what I posted again, please!

koendd · « **Reply #19 on:** October 30, 2015, 09:10:26 AM »

well maybe I explained it wrong...

Doesn't pop just while idling. But after full throttle and releasing...
not when just standing still..

flybox1 · « **Reply #20 on:** October 30, 2015, 09:51:04 AM »

OK.
You'll need to complete a series of plug chops with NEW plugs, beginning with a WOT plug chop to see if your 110 main jets are correct.
Please take the time to read up on how to properly do a plug chop, and make the necessary changes to your main jet, if needed.
Once main jet is correct, then move on to a 2/3 throttle position chop, make needle clip changes as needed.
Then on to 1/4 throttle position chop to check for proper pilot jet sizing, and change as necessary.
Lastly, idle chop for mixture screw setting followed by a vacuum sync.
It'll take 6 +/- sets of plugs....lean (white) plugs can be reused for the next chop.
If you complete the above accurately, your bike should pull hard at all throttle positions and to red line.

koendd · « **Reply #21 on:** October 30, 2015, 10:40:31 AM »

Quote from: flybox1 on October 30, 2015, 09:51:04 AM

OK.
You'll need to complete a series of plug chops with NEW plugs, beginning with a WOT plug chop to see if your 110 main jets are correct.
Please take the time to read up on how to properly do a plug chop, and make the necessary changes to your main jet, if needed.
Once main jet is correct, then move on to a 2/3 throttle position chop, make needle clip changes as needed.
Then on to 1/4 throttle position chop to check for proper pilot jet sizing, and change as necessary.
Lastly, idle chop for mixture screw setting followed by a vacuum sync.
It'll take 6 +/- sets of plugs....lean (white) plugs can be reused for the next chop.
If you complete the above accurately, your bike should pull hard at all throttle positions and to red line.

excellent!

koendd · « **Reply #22 on:** October 30, 2015, 01:12:16 PM »

so. Set all the needles back to second top groove (should be the stock position as read on hondachopper http://www.hondachopper.com/garage/carb_specs/carb_specs.html)

while I was at it checked the idle mix screws and the one on 3Th cil had a broken O-ring. replaced that one, let's see if things are better now...

754 · « **Reply #23 on:** October 30, 2015, 06:06:55 PM »

If you have xhaust leaks you will have popping on decelleration.

koendd · « **Reply #24 on:** October 30, 2015, 11:11:00 PM »

I have installed new exhaust gakets as well...

any way to check if it leaks? can see/feel any leaks...

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Author Topic: false air CB750 F2 (Read 3540 times)