High Revving & Idle Problems

[Anonymous]

I started my bike again after a number of other starts and stops in the process of getting this 850L on the road. Unfortunately, on it's own, the bike likes to rev around 3000+ rpm at times. Here's a brief synopsis of the path that brings me to where I am today.

1. The carbs have been thoroughly cleaned as per the website's instructions.

2. The bike used to leak fuel out the carbs until I replaced the vacuum petcock with a manual one from Pingel. I also adjusted the floats during the carb cleaning.

3. I removed the inline filter (with a "stone" in it) that the previous owner installed in the fuel line.

4. I replaced the oil and the filter that had fuel in it from the leaking petcock.

When I went to start it today, I had to prime the carbs with some shots of gas from a spray bottle, as it wouldn't start otherwise. When it did start, it rocketed up to 4000 rpm, at least, and would not come down, even after backing the idle screw all the way off.

I shut the bike down, and then remembered the throttle cable adjusters by the throttle itself. I backed those off as well and then reset the the idle screw. This time the bike started and did not rev so high and was more responsive to additional adjustments to the idle screw.

However, after setting the idle screw and the throttle adjusters, I revved the engine to see how it responded, and it would not come down below 3000. It just seemed to hang mostly around 4500 just screaming away.

So I tried adjusting the idle screw and throttle adjusters again, but just kept getting the same thing again and again. When I think it's adjusted, and I have the bike idling around 1000 rpm, I give it some gas and it jumps up to 3-4000+ rpm and just likes to stay there.

I read through Detman's posts and threads from back in March when something similar happened to him. But unlike his situation, my petcock is now manual and doesn't leak.

From some of Detman's own suggestions, I am considering float levels (again), sticking slides, and/or leaking boots. Of course, any other suggestions are always welcomed.

Thanks in advance.

[Anonymous]

It could be an intake leak or you just need to sync your carbs.

Steve

[earlfor]

Re: High Revving & Idle Problems

Since the engine is designed to start and idle with no application of the throttle at all, try this.
1. Disconnect the throttle cable (incorrect throttle cable adjustment will now not be a possibility.

2. Unscrew the idle adjustment knob until it no longer is in contact.

3. Remove your carb stack and set the throttle plate adjustment screws and visually check that all slides are all the way down. Then turn the adjustment screws until you can see the slide START to move back up. Back off adjustment screw about 1/2 turn. Reinstall carbs on bike. Make certain there are no induction tube leaks on the engine or airbox side.
make sure airbox is sealed and has a filter in it.

4. Start engine using only the choke as an enrichener and throttle control.

5. Once running, turn in idle adjustment knob until 1200 rpm shows on tach with choke off. Decrease adjuster knob or decrease choke to maintain no more than 1200 rpm. Once warm, adjust knob for 1200 rpm without choke. If you cannot do this, then your idle circuits are not functioning.

Note:............. Above aprox 1500 rpm, idle adjustment screws/circuits are no longer priority and have little to no effect on altering rpm.

Once you get the engine to idle and run somewhat normally, you will need to synch the carbs with vacuum stiks/guages as, "byguess and by golly, eyeball" is a truly haphazard waste of time.

Earl

[Anonymous]

Sounds like some sync-ing is in order. What is a good source for an appropriate tool to sync the carbs? I gather from other posts that the mercury type tool is recommended.

Also, what exactly is the idle circuit? For that matter, what are the circuits in the carb? I did copy down someone's helpful diagram showing which components came into play at different RPMs, but I wouldn't pass up an opportunity for a little Carb 101 if someone has the time and interest.

Much thanks

[earlfor]

You can buy a mercury carb synch stix from http://www.crc2onlinecatalog.com/ for about $40.
Their price is as good or better than most anyone else.
You will want the "kit" with the 5 mm adapters.

The idle circuit provides fuel/air at low rpm when the throttle plate/butterfly is closed or slightly open. Fuel is picked up from the float bowl through the main jet and metered by the pilot jet and mixed with air coming in through the pilot air jet. The mixture then goes through the pilot pipe to the pilot screw and then the mainfold intake. This is the idle/slow speed circuit.

After this, there are intermediate and main jets and a movable needle (slide/piston needle) They all work together, but at different rpm, different proportions of each will be working. They overlap each other in their functions. Basically, you would call this combination of jets and movable needle the main system. It works more or less like this. When the throttle valve is opened, engine rpm increases and causes an increase in vacuum in the venturi. The fuel from the float chamber is regulated by the main jet and enters the needle jet where it is mixed with air from the main air jet creating a mixture. This mixture goes through the clearance between the needle jet and jet needle and goes into the intake airstream into the engine. Throttle position causes a change in intake velocity(vacuum), which alters fuel draw relative to intake air volume.
(all this says is if you twist the throttle, you go faster ....:-) )

Earl

Sounds like some sync-ing is in order. What is a good source for an appropriate tool to sync the carbs? I gather from other posts that the mercury type tool is recommended.

Also, what exactly is the idle circuit? For that matter, what are the circuits in the carb? I did copy down someone's helpful diagram showing which components came into play at different RPMs, but I wouldn't pass up an opportunity for a little Carb 101 if someone has the time and interest.

Much thanks