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RPM's fall when pressing the rear brake??

Started by ryanschoebel, March 28, 2019, 01:26:13 PM

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ryanschoebel

Yeah, you read that right. I'm thoroughly confused. On the new 84, when i stop at a stoplight, the bike idles at about 1200. But after a few seconds, the idle will bump up to about 1500-1600. If I press the rear brake, the idle will settle right back down to 1200. As soon as i take my foot off the brake, it goes right back up. I see NO way for those two systems to be interconnected. Thoughts??

Thanks,
Ryan
1985 FJ1100-- Atlas (SOLD)
1984 FJ1100-- Storm

Pat Conlon

You are correct, no interconnection between brakes and carbs. 1200 idle is too high. Adjust idle down to 1,000. Do blip test for air idle adjustments. If idle is good at start, then increases as engine warms up, it is rich. If idle is good at start then decreases as engine gets hot, it is lean. Check for vacuum leaks. Do suck test on #2 vacuum line that goes to the TCI. Should be tight.
1) Free Owners Manual download: https://tinyurl.com/fmsz7hk9
2) Don't store your FJ with E10 fuel https://tinyurl.com/3cjrfct5
3) Replace your old stock rubber brake lines.
4) Important items for the '84-87 FJ's:
Safety wire: https://tinyurl.com/99zp8ufh
Fuel line: https://tinyurl.com/bdff9bf3

ribbert

Quote from: ryanschoebel on March 28, 2019, 01:26:13 PM

........ If I press the rear brake, the idle will settle right back down to 1200. As soon as i take my foot off the brake, it goes right back up.

Thanks,
Ryan

Does the actual idle speed change or just the tacho reading?
Did you repeat this enough times to establish a pattern or was it a one off coincidence?

Noel
"Tell a wise man something he doesn't know and he'll thank you, tell a fool something he doesn't know and he'll abuse you"

ryanschoebel

Quote from: ribbert on March 28, 2019, 06:15:48 PM
Quote from: ryanschoebel on March 28, 2019, 01:26:13 PM

........ If I press the rear brake, the idle will settle right back down to 1200. As soon as i take my foot off the brake, it goes right back up.

Thanks,
Ryan

Does the actual idle speed change or just the tacho reading?
Did you repeat this enough times to establish a pattern or was it a one off coincidence?

Noel

The actual idle speed. And i did it about a dozen times, to make sure i wasnt imagining it. It happens every time.
1985 FJ1100-- Atlas (SOLD)
1984 FJ1100-- Storm

RPM - Robert

stepping on the brake adds an electrical load which can draw down the engine speed.

Did you keep your carbs from Atlas...?


ryanschoebel

Quote from: RPM - Robert on March 28, 2019, 07:42:37 PM
stepping on the brake adds an electrical load which can draw down the engine speed.

Did you keep your carbs from Atlas...?



Unfortunately, no. I figured I would just send you guys this set within a few months. Suck test is good, no leaks. It hold pressure well. How do I do the blip test?
1985 FJ1100-- Atlas (SOLD)
1984 FJ1100-- Storm

Pat Conlon

In the blip test you are checking to see if you have a hanging idle or idle dip.
This is the final test you do to set your air/fuel idle adjustments.
Adjust the valves.
Balance your carbs. (assuming clean heathy carbs)
Set your idle speed @1k
Hook up your aux tank, you need the tank off for access to the carbs.
Start, warm the bike up.
Blip the throttle,
1) when throttle is snapped shut, does the engine rpm hang at high rpms before slowly returning to idle rpm?
Too rich, turn idle air/fuel screws in (clockwise)

2) when throttle is snapped shut, does the rpm drop below idle speed then slowly rise to idle rpm?
Too lean, turn air/fuel screws out (counterclockwise)

Adjust in 1/4 turn increments.


1) Free Owners Manual download: https://tinyurl.com/fmsz7hk9
2) Don't store your FJ with E10 fuel https://tinyurl.com/3cjrfct5
3) Replace your old stock rubber brake lines.
4) Important items for the '84-87 FJ's:
Safety wire: https://tinyurl.com/99zp8ufh
Fuel line: https://tinyurl.com/bdff9bf3

ryanschoebel

Thanks Pat, I'll try that after work tomorrow. Tim says carbs were done, but that was 18 months ago. Any number of seals could have corroded. I hate to be that guy, but the idle air fuel screws are the screws that i see just to the engine sides of the carbs, right on top?
1985 FJ1100-- Atlas (SOLD)
1984 FJ1100-- Storm

FJmonkey

Remember to keep air moving on your engine with a fan or two. Air cooled engines can idle for only so long with no moving air to cool it, till they over heat.
The glass is not half full, it was engineered with a 2X safety factor.

'86 Ambulance - Bent frame, cracked case, due for an overhaul
'89 Stormy Blue - Suits my Dark Side

Pat Conlon

It sounds like you have it..




A - This is the idle mixture adjustment screw.  Each carb has one.
1) Free Owners Manual download: https://tinyurl.com/fmsz7hk9
2) Don't store your FJ with E10 fuel https://tinyurl.com/3cjrfct5
3) Replace your old stock rubber brake lines.
4) Important items for the '84-87 FJ's:
Safety wire: https://tinyurl.com/99zp8ufh
Fuel line: https://tinyurl.com/bdff9bf3

aviationfred

I'm not the fastest FJ rider, I am 'half-fast', the fastest slow guy....

Current
2008 VFR800 RC46 Vtec
1996 VFR750 RC36/2
1990 FJ1300 (1297cc) Casper
1990 VFR750 RC36/1 Minnie
1989 FJ1200 Lazarus, the Streetfighter Project
1985 VF500F RC31 Interceptor

ryanschoebel

Quote from: Pat Conlon on March 28, 2019, 11:39:28 PM


A - This is the idle mixture adjustment screw.  Each carb has one.


Perfect, thats the one I thought. Thanks all, I'll let you know how it goes tomorrow
1985 FJ1100-- Atlas (SOLD)
1984 FJ1100-- Storm

Flynt

At the risk of a tongue lashing about how carbs can't be cleaned without taking them off, I've found that the occasional bottle of Techron in the tank does fix some minor fueling issues due to partially blocked jets...  my '84 has the stock carbs and the combination of running Chevron fuel and adding a bottle of Techron every few months has kept it running well for the past few years since carbs were gone through.  After not riding it for a few weeks, I add the Techron to minimize the buildup of gunk from the dried fuel...  If you have a slightly lean condition (matches your symptoms), the Techron might just do the trick by removing some of the fuel system deposits.

Interestingly, I've found the flatsides on the '92 react quickly to the Techron treatment.  Several times over the years it has started to run poorly, especially at low speed...  Add the Techron and it's always fixed itself within that tank full.

In short, you might try a bottle of Techron and a tank of high quality fuel before you start into carb adjustments.

On a related note...  do your carbs have flat bottomed slides?  If so, you have a unique beast and I might have the jet sizes/adjustments you need.  Randy told me I'm the only person he knows of that actually tuned the flat bottoms instead of swapping to the curved bottom slides.  Stormy (my '84) runs beautifully...

Frank

There's plenty of time for sleep in the grave...

RPM - Robert

Quote from: Flynt on March 29, 2019, 09:52:11 AM
At the risk of a tongue lashing about how carbs can't be cleaned without taking them off, I've found that the occasional bottle of Techron in the tank does fix some minor fueling issues due to partially blocked jets...  my '84 has the stock carbs and the combination of running Chevron fuel and adding a bottle of Techron every few months has kept it running well for the past few years since carbs were gone through.  After not riding it for a few weeks, I add the Techron to minimize the buildup of gunk from the dried fuel...  If you have a slightly lean condition (matches your symptoms), the Techron might just do the trick by removing some of the fuel system deposits.

Frank

Bring out the pitchforks! :diablo:

But yes some sort of fuel additive definitely helps with the fuel problems from sitting. Check out fuel phase separation http://www.lcbamarketing.com/phase_separation_in_ethanol_blen.htm

ryanschoebel

Quote from: Flynt on March 29, 2019, 09:52:11 AM
At the risk of a tongue lashing about how carbs can't be cleaned without taking them off, I've found that the occasional bottle of Techron in the tank does fix some minor fueling issues due to partially blocked jets...  my '84 has the stock carbs and the combination of running Chevron fuel and adding a bottle of Techron every few months has kept it running well for the past few years since carbs were gone through.  After not riding it for a few weeks, I add the Techron to minimize the buildup of gunk from the dried fuel...  If you have a slightly lean condition (matches your symptoms), the Techron might just do the trick by removing some of the fuel system deposits.

Interestingly, I've found the flatsides on the '92 react quickly to the Techron treatment.  Several times over the years it has started to run poorly, especially at low speed...  Add the Techron and it's always fixed itself within that tank full.

In short, you might try a bottle of Techron and a tank of high quality fuel before you start into carb adjustments.

On a related note...  do your carbs have flat bottomed slides?  If so, you have a unique beast and I might have the jet sizes/adjustments you need.  Randy told me I'm the only person he knows of that actually tuned the flat bottoms instead of swapping to the curved bottom slides.  Stormy (my '84) runs beautifully...

Frank



Where would I buy said techron? I usually just run Seafoam through my carbs. As for gas, I only run premium, but it is still ethanol fuel.

That said, I was thinking about it last night and today, and i have questions about using an aux tank for the testing. If i hang a tank, and just run hose to the carbs, wouldn't that flood it? Don't i need some sort of impedance, IE, the petcock in line to make sure it isnt flooding from constant fuel? What sort of aux tanks have people used?
1985 FJ1100-- Atlas (SOLD)
1984 FJ1100-- Storm