Fuel Milage

[dingy]

Installed two new plugs in the front cylinders, 4 more oz. of Sea Foam. Performed the 30 sec. run test. Front two cylinders might have been a little warmer (my pyrometer fingers). Fuel gauge says half a tank (three bars)(it has to be a 4 gallon tank) Trip odometer is on 70. I'm gaining on the mpg. When I get real ambitious, I'll tweak on the slide needles.

 

It is a 5.3 gallon tank on 1st gens.

 

Gauge reading is not linear. It takes a while to drop the first bar, and the last bar goes fairly quick. Through the mid range of gauge, there is more mileage between bars.

 

Dingy

[skydoc_17]

Hey Gilbert,

Adjustment of the Idle Mixture Screws (see pic) which are found in the body of the Carb. is not the same as re-shimming the Main Jet Needle. For the early MKI models, (83/some 84) the main jet needles are adjustable, for all other years the main jet needles must be shimmed. Here is a link to the kit:

http://www.venturerider.org/classifieds/showproduct.php?product=2711&title=needle-shim-mod-nylon-spacers-21&cat=6

 

If you have questions or need parts, feel free to PM me.

Earl

[greg_in_london]

About the needles - there are different part numbers for different years and different market places. According to the Mikuni specialists I spoke to when I researched all this a couple of years ago, the numbers in the designation list the diameters and slopes/gradients on the needles.

 

That would indicate that needles are not interchangeable - or at least would change the charcteristics markedly. This might be positive or might be negative, depending on what you have and what you get.

 

If you don't have the adjustable needle, you could check out the other thread on the shim under the needle clip - but finish cleaning everything out first and also consider checking the o-ring around the nozzle and replacing the rubber bungs in the jet block (this is what I'm doing over the next few days - I'll take pictures if you need them).

[Condor]

Check the choke linkage to make sure that the enriching rods are able to come all the way out. A partial choke will really screw up the milage. Also Sea-Foam will clean out the carb jets, but it won't make the fuel any more effecient. MOF after running the first SF mix the plugs will probably need to be changed again... Also sounds like a good sync is in order...

[GilbertHall]

The previous owner gave me his Topeka Powersports receipt. They charged him for the diaphragm assemblies and one hour of labor to install them. I would think the technician would sync the carbs, because the service writer wrote the work order as poor fuel mileage. Would syncing the carbs show up as a separate line item on the receipt? Is one hour enough time to install the diaphragm assemblies and sync the carbs?

[jasonm.]

Syncing the carbs should be listed separate. BUT the idle sync will not change much by replacing diaphragm slides. Sync is the amount of vacuum when the throttle are closed. BUT a good mechanic should ALWAYS be checked at partial openings from 2000 to 4000rpm. I had recent carb issues. Here is what I found in my case and many disassemblies. One bad float needle for sure , but changed 2 . Bad float...getting soft when submerged in gas. To check, you must fully submerge for 2-5 hours min. and check for SOFT spots. I also found all of the choke plungers were closing but some where NOT sealing. The aluminum body of the choke can get pitted or the plungers rubber seals can just be worn out. FYI, we 1st gens are all running on worn needle jets. Shimming the needles helps during real "normal" running. BUT having these worn needle jets will always cause richness on hard acceleration...depending on how far you twist the throttle. The true cure to get back the "NEW bike" mileage at all throttle openings, is replacement of the needle jets. Which is quite involved. So shimming is the next best thing. Now that I had my bike EGA'd on the $15k variable load dyno. It's running very good. 44+ mpg on the back roads and yet to be checked on the hiway. I think 40mpg is now possible at my usual 70+mph rides. It was an eye opening experience doing this tuning. Which I did all the labor. The Dyno guy just twisted the throttle and played with the computer for load and other bits. FYI- the low speed screws can be anywhere from 1.5 to 2.5 turns out. Every carb and bike is different. I was told K&N sells less expensive needle jets that will work, compared to the Yamaha dealer. Once I got it tuned,this helped me figure out. I have a bad coil or 2. ANYONE have some spare good coils? To be a perfectionist...I may replace all my needle jets....next year:mo money:.

Edited July 20, 2010 by jasonm.

[bkuhr]

I also found all of the choke plungers were closing but some where NOT sealing. The aluminum body of the choke can get pitted or the plungers rubber seals can just be worn out. .

 

How do you test for leaking choke enrichers?

I have two cylinders very rich and this sounds like a possibility?

[jasonm.]

You have to have a GOOD digital tach. Norhthern Tools sells one for about $40. TO TEST-for the issue...shortly after start up...say a minute or 2. Your bike should idle NO CHOKE. Then CHOKE OFF, one by one you press down with your finger firmly on the choke plunger. If the tach shows an idle change of more than 10 or 20rpm or more. Your choke is leaking. Cold idle shows this most clearly.You must remove the carbs to address the choke plunger conditon. It can be somewhat repaired...depending on the cause. My bike is tuned so well. I can start it cold with a little choke and turn it off choke in less than 1 minute , it will idle smooth but slow. Others say they can do this too. But MOST are just rich at idle and that's how they are capable of doing it. Mine is EGA's at 13.7 : 1 air/fuel. Prior to this is was 12.5 :1 or worse on some of the cylinders. 13:1 give best power. But closer to 14:1 gives economy with more than enough power. So you split the difference. 13.7:1 is close to 2% CO. And 1.5 to 2% CO is what the Venture likes. I used to work in a shop in the 80's. Let me know if yours passess the above test...In my case both the choke plungers were leaking and a float and float needle issue accured.

Edited July 20, 2010 by jasonm.

[CrazyHorse]

Syncing the carbs shold be listed separate. BUT the idle sync will not change much by replacing diaphragm slides. Sync is the amount of vacuum when the throttle are closed. BUT a good mechanic should ALWAYS be checked at partial openings from 2000 to 4000rpm. I had recent carb issues. Here is what I found in my case and many disassemblies. One bad float needle for sure , but changed 2 . Bad float...getting soft when submerged in gas. To check, you must fully submerge for 2-5 hours min. and check for SOFT spots. I also found all of the choke plungers were closing but some where NOT sealing. The aluminum body of the choke can get pitted or the plungers rubber seals can just be worn out. FYI, we 1st gens are all running on worn needle jets. Shimming the needles helps during real "normal" running. BUT having these worn needle jets will always cause richness on hard acceleration...depending on how far you twist the throttle. The true cure to get back the "NEW bike" mileage at all throttle openings, is replacement of the needle jets. Which is quite involved. So shimming is the next best thing. Now that I had my bike EGA'd on the $15k variable load dyno. It's running very good. 44+ mpg on the back roads and yet to be checked on the hiway. I think 40mpg is now possible at my usual 70+mph rides. It was an eye opening experience doing this tuning. Which I did all the labor. The Dyno guy just twisted the throttle and played with the computer for load and other bits. FYI- the low speed screws can be anywhere from 1.5 to 2.5 turns out. Every carb and bike is different. I was told K&N sells less expensive needle jets that will work, compared to the Yamaha dealer. Once I got it tuned,this helped me figure out. I have a bad coil or 2. ANYONE have some spare good coils? To be a perfectionist...I may replace all my needle jets....next year:mo money:.

 

Precisely, which needles are you talking about?

[jasonm.]

The needles are in the slide/diaphragm assembly. These needles are removable because they are very expensive and the slides are usable on other carbs. I believe they are titanium needles. There are othe posts showing the shimming process. Being the needle jets brass and the needle titanium. The brass gets worn out. You need a hollow torx bit to get one of the slide caps' screws off. Then a standard torx works. There is a tab/bump the makes the stock shim .12" thick. Some have removed the little bump. to make it .100 thick. Some have been able to dremel or sand the BUMP off. ME, I just found the proper shims to make it just about .100". Which was good per the dyno runs. The needle-jets(brass) wear. The needles(titan) don't.THESE ARE THE ONLY needles in you carbs.

Edited July 22, 2010 by jasonm.

[CrazyHorse]

The needles are in the slide/diaphragm assembly. These needles are removable because they are very expensive and the slides are usable on other carbs. I believe they are titanium needles. There are othe posts showing the shimming process. Being the needle jets brass and the needle titanium. The brass gets worn out. You need a hollow torx bit to get one of the slide caps' screws off. Some have been able to dremel the center "nipple" off. Then a standard torx works. There is a tab/bump the makes the stock shim .12" thick. Some have removed the little bump. to make it .100 thick. ME, I just found the proper shims to make it .100". Which was good per the dyno runs. The needle-jets(brass) wear. The needles(titan) don't.THESE ARE THE ONLY needles in you carbs.

Ok thats what I thought you were talking about.

[GilbertHall]

It is a 5.3 gallon tank on 1st gens.

 

Gauge reading is not linear. It takes a while to drop the first bar, and the last bar goes fairly quick. Through the mid range of gauge, there is more mileage between bars.

 

Dingy

 

So when the warning light comes on, I still have approximately 1.3 gallons left?

[Squidley]

So when the warning light comes on, I still have approximately 1.3 gallons left?

 

 

More like a gallon or just a bit under that, when the light comes on you better be getting gas within the next 30 miles.

[jasonm.]

I have calibrated my sending unit ...that when the light stays on, up or down hills(I have many here). I have 1.1 gal. +/- .1

[GilbertHall]

Thanks Sky doc 17! 37.6 mpg:dancefool:Idles slower, no more bog between 2,000 & 3,000 rpm, smoother starts. Back in 91', I had access to 4 vacuum guages (especially for syncing motorcycle carbs) Can I get by with two guages, being how you sync to #1 anyway?

[Trader]

I sent you an email!