Help with idle problem!

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apezman07
Posts: 5
Joined: Sat Dec 21, 2019 1:16 am

Help with idle problem!

Post by apezman07 »

The idle won't stay in one spot. It will hold at a certain rpm, then when I rev the bike, the idle will stick up high and then hold there for a while until slowly falling. I turn the idle adjuster and it will change the idle but doesn't help it hold at one rpm. The bike runs great while I'm riding and has tons of power; only having this issue at idle. If I adjust the idle screw down too far, the bike will stall as idle falls; if this happens then I have to add throttle while cranking the bike over for it to start.

Modifications to bike:
-2 into 1 exhaust
-PAIR valve deleted and block off plates installed
-TPS adjusted to somewhere around 500-600 ohms
-180 front jet, 185 rear jet
-dynojet adjustable needles set at lowest setting (closest to point of needle)
-all 3 lift holes in the slides are drilled out
-re routed carb breather lines so they point down
-I have 2 sets of slide springs, short and long. long ones are installed but the bike acts the same way with short springs installed

Mixture screws are 2.5 turns out on both carbs. Throttle cable is not sticking (not sure if butterflys and/or linkage isn't sticking). Airbox is factory. Fuel floats are non-adjustable.

The bike was doing the same thing BEFORE 2 into 1 exhaust was installed, tps adjusted, slide holes were drilled out, carb breather lines were re-routed, and regardless of what length slide springs are installed.

Also, am I correct in having the front jet leaner than the rear jet, and should I adjust the mixture screws differently or have them both at the same setting?
98 Hawk:
Carrozzeria rims,954rr front end & triple,1000rr tail,2 into 1 exhaust & Yoshimura can,15/44 gearing

93 Intruder 1400:
Drag pipes,forward controls,custom handlebars & risers,custom intake,custom rear running lights,chrome everything
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popkat
Posts: 2804
Joined: Sat Apr 28, 2012 9:32 am
Location: Devon

Re: Help with idle problem!

Post by popkat »

Usual cause is an air leak on the inlet.
Tight valve clearance could contribute

With the mixtures get an exhaust gas analyzer and adjust to about 4% co.. Not so easy to do on the twin pipe system but with your 2 into 1 it should work.



.
http://www.bidefordmotorcycles.co.uk
2014 CRMC Post classic Superbike champion.
2014 CRMC Post classic senior production champion. On a Suzuki Katana 1100
My bikes, Firestorm, Suzuki GSX-s1000 Katana, VFR800Fi. Projects, 1986 popup Katana, 3 XJ600’s
jchesshyre
Posts: 590
Joined: Wed Jun 15, 2016 9:09 am
Location: Chester, Cheshire

Re: Help with idle problem!

Post by jchesshyre »

What he said, and also check the throttle linkage as I had this issue before and it turned out to be caused by slop/play in one of the throttle linkage pivot points that had a stripped nut on that wouldn't do up properly.
tony.mon
Posts: 15938
Joined: Wed Jul 25, 2007 10:46 pm
Location: Norf Kent

Re: Help with idle problem!

Post by tony.mon »

Also check throttle linkage bar is not being caught by one of the rubber drains or vacuum pipes.
Lastly, check that the twist grip/throttle rubber isn't catching on the bar ends, and that the cable isn't fraying inside the outer sleeve.
It's not falling off, it's an upgrade opportunity.
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fabiostar
Posts: 7541
Joined: Sat Jun 01, 2013 3:53 pm
Location: sunny belfast

Re: Help with idle problem!

Post by fabiostar »

spay a load of easy start in round the cabs and carb rubbers when its ticking over, if the revs dont rise that will rule out any air leaks. :thumbup:

and generally your fuel screw setting should be a little more screwed out on the rear than the front, maybe a quarter to half a turn more on the rear
the older i get,the faster i was :lol:
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kenmoore
Posts: 652
Joined: Sat Feb 11, 2012 8:25 am
Contact:

Re: Help with idle problem!

Post by kenmoore »

Second the different mixture setting on the rear cylinder.

Don't know why but it works !

Took me 8 years to work this out!

Bloody travesty. :beer: :beer: :beer:
South Coast
New South Wales
Australia
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apezman07
Posts: 5
Joined: Sat Dec 21, 2019 1:16 am

Re: Help with idle problem!

Post by apezman07 »

I found the solution to my problem. I'll explain in hopes that it'll help someone else.

I have 2 hawks, one with a blown motor and 1 that runs. 2 different carb setups and 2 of everything so it was easy to swap things in and out to see what worked best. Note the airbox and air horns are factory.

The one that runs, when I bought it, it had dynojet adjustable needles (with the 6 grooves). The needles were on the very bottom groove, as rich as they could go. There was an additional lift hole drilled into the slide & needle retainer. Note that the factory lift holes were covered by the needle retainer. Factory slide lift springs. Front jet 180, rear jet 185. Mixture screws were who knows where. There was an existing idle issue, where the idle would rise above where it should be and not maintain an even idle around 1100rpm.

I took the carbs apart, cleaned everything, and reinstalled the 180/185 jets. I kept the needles on the 6th groove. I installed the needle retainers from my blown hawk- 3 lift holes in the slide and an accompanying 3 holes in the needle retainer (this is where I went wrong). I also installed the dynojet shortened slide lift springs. Mixture was somewhere around 2.5 turns out.

When I fired the bike up, it had the same idle issue but now worse. So after probably 10 times tearing the carbs apart trying different things, many mixture settings, and quite a few full throttle passes, I figured out the issue:

For starters, the needles should not have been in the 6th groove. Every time I adjusted them back (went leaner), the idle issue would get better. I finally settled in the 4th groove from the top- the 3rd grooved required the mixture screws to be turned out too far and it made less power than the 4th groove anyways, regardless of where the mixture screws were at.

Another big issue was I had too many lift holes in the slides. I finally went back to the original needle retainers with only 1 hole drilled (instead of 3). Note there are still 3 lift holes in the slides, but the 2 factory holes are covered by the needle retainer.

I inevitably went back to the longer factory slide lift springs, in lieu of the shortened dynojet ones. However, I'm not sure if this made a big difference or not.

I ended up with the mixture screws 2.75 turns out in the front, and 3.00 turns out in the rear. I'm not saying this is the perfect mixture, but it sure pulls hard as hell and I have power all through the rpms; no dead spots or sputtering. As well as a good, steady idle and perfect running condition in stop and go traffic. Every now and again it'll "cough" when I grab throttle hard at idle with the clutch pulled in or bike in neutral (I figured I can live with this in lieu of the idle issue and the fact that it doesn't happen often anyways). If I go a quarter turn leaner on the mixture, it has a very subtle lean pop from the exhaust. A quarter turn richer and it has a heavy gas smell from the exhaust. That's why I settled with the mixture where it's at.
98 Hawk:
Carrozzeria rims,954rr front end & triple,1000rr tail,2 into 1 exhaust & Yoshimura can,15/44 gearing

93 Intruder 1400:
Drag pipes,forward controls,custom handlebars & risers,custom intake,custom rear running lights,chrome everything
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Chris58
Posts: 123
Joined: Tue Aug 01, 2017 2:57 am
Location: Canada

Re: Help with idle problem!

Post by Chris58 »

Good to see you sorted that out. Not fun tearing the carbs off 10 times.. but worth it in the end

I installed a wide band sensor in my exhaust with a guage so I can read my mixture as I ride.. great way to monitor your mixture.

Here's how mine went:

-185 front and 190 rear

-45 pilots, 2 turns out

-Long OEM springs

-One extra lift hole drilled

-Needle clip at 3rd position when I used dynojet, I've since put OEM needles back with a .040 washer under them. Runs way better like that.

-Airbox gutted with filter in lid.

-I also put on one of those air commanders to control the air allowed into the mixture, works like a fine adjustment for mid range, and top end mixture

This setup probably won't work for most people, It all depends on mods you have done, elevation, etc.
There's so many variables to get it right, everyone has/needs a slightly different setup
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