jimdi
Jimdi
I have learned this from the school of hard Knocks and from Working on Carbs via email with XS John - God Bless him... I miss our discussions...
I posted it years ago - but a rough idle brought it up in my mind so I am re-posting it - hopefully it will save someone some work. This isn't everything - just some common answers to common problems. I don't get into Needles or re-jetting here - just getting the bike to run smooth.
I have an 81 with 34's:
135 MJ - 135 Airjets
45 idle jets
John's needles - Canadian jets.
Runs GREAT!
I have a set of stock 34mm for my 81 Heritage 650 special - and for kicks a bought a second pair - for back up and to experiment with.
Here are some tricks to some problems I ran into that helped me –
Start with Problems –
Rough Idle?
Look at Spark Plugs - Are Plugs Wet? If Yes Look at Floats / Needle Valve First.
Are Plugs Dry? Look for Air Leak near Carbs – OR Clogged Pilot Jet Passage – Or Incorrect Fuel / Air Mix.
(Try this first – Get some Good Carb Cleaner – Spray Type – and put the "straw"into the Pilot Jet opening and the Main Jet Opening One at a time and blast the passage.) (They are located on the air filter side of the Carb at the throat opening– round holes at 4 and 8 O'clock. )
Here are some Other tips that helped me...
Tips for beginners.
1 - get a book
2 --do one carb at a time -
3- view just about evey post in the fuel sections for tips.
To set idle air – fuel mix
Carbs mix air and gas - as I recall the perfect mixture is 14 to 1.
Too lean (too much air) causes hesitation, knocking, poor idle and heat -
Too rich (too much gas) causes plug fouling, backfire.
As a general rule with any carb - gently screw the idle mixture screw in until seated counting the turns clockwise. WRITE IT DOWN>
Then unscrew the screw to that point or 1.5 turns.
Start the engine - slowly 1/4 turn at a time screw in until the engine rpm drops - this is lean roll off - note the turns in. Now unscrew past optimum idle until the rpm drop from too much fuel - this is rich roll off - again note the turns out - Mix should be set dead center of these 2 figures --- for example -
Lean roll off 1
rich roll off 3
Ideal is 2
Rebuilding:
So far what I have seen here is that - if it has an O ring replace it.
foam floats like a float level of about 22-24mm - but it varies from carb to carb. The yamaha manual has lots of information about the carbs - you can get it free here
www.biker.net/650parts_index.html
Notice the section on checking the float level with a clear tube (done on bike)
Take a clear tube and attach it to the drain nipple on the bowl of the 34 carbs with the bike LEVEL! Loop the tub up the side of the carb like a big J. Put the fuel petcock on PRIME and open the drain screw on the carb bowl. Fuel will flow up the tube. If floats are correct the fuel should stop at the top of the bowl right below (1-2mm) the seam between the bowl and the carb body.
DON'T MESS WITH THE FLOATS -- IF THEY ARE WORKING.
Concentrate on cleaning the Jets and passage ways.
Check the diaphrams - for tears (see below)
remove all the jets and clean them with compressed air - check passages by viewing light through the holes.
Be gentle! Brass bends easily.
Other Helpful stuff...
1- floats - judging by the condtion of the float pins in both sets - I can see that people have trouble removing pins that have been in for a while - simple solution - use a fine drill bit the slightly smaller than the diameter of the pin - and gently tap out the old pin using the drill bit as a "drift." I mount my carbs sideways in a vise (clamping on the angle iron that joins the two carbs) line the drill bit up with the end of the pin opposite the T and tap the drill bit lightly until the pin is pushed out. The smaller drill bit then easily pulls back out through the hinge.
One more note:
I discovered that the replacement foam floats from MIKES actually bind in the float bowl - not good. Hinge is loose on the pin.
I love mikes to buy stuff - but if you use these floats - they will require modification.
A small brass tube from a hobby shop works well to shim up the difference between the floats hinge and the stock pin.
2- float levels – Buy a micrometer at harbor freight for $20 it's a must for carbs.
on 34mm - the factory float setting of 27mm is just WRONG. 22-24mm with no gasket is dead on. Also when comparing both float levels - check them both at rest (normal) not compressed - both sides should be equal (height while depressed doesn't matter as long as they are equal). Bending the tang to adjust the floats can effect the level of the how evenly they close - so they may match at rest - but don't match at operation.
3) Bench testing floats - mount your carbs in a vise (as per above -by angle iron between carbs) Use a level to make sure they are level at rest.
Take your 2 gallon lawn mower gas can and set it on a shelf higher than the carbs. Run a 1/4 siphon tube from the gas can to the carb gas intake and let them fill (siphon action from can to carbs)
Attach a clear tube to the drain nipple on the bowl, and open the drain screw - hold the clear tube up to the edge of the bowl (it will now be U shaped) and compare the gas level to the side of the bowl - repeat for both carbs - both gas levels should rise to about 1mm below the TOP edge of the float bowl - AND both sides should be equal. This save the trouble of mounting and removing the carbs - each time you need to adjust the float levels.
4) Diaphrams - Close the Choke! Put your thumb over the large opening on the top of the AIR cleaner side of the carb - push the diaphram / needle assembly in the throat of the carb UP - and release it while keepin the hole covered. The assembly should hold in place or fall VERY slowly - if not - you have a leak.
5) Float hinge - make sure the brass insert is in the float hinge - many aftermarket ones are missing the insert and cause the floats to ride floppy on the pin - re-use the old insert - or fashion a new one from brass tubing from a hobby store to clean up the action.
6) Idle mixture screw O ring - After removing the brass plug - and counting the factory number of turns until the needle is gently seated - your should remove the needle for cleaning. Often it leaves the O ring and washer still in the hole. Use a small paper clip - with the end bent into a J to gently fish out the old O ring and washer.
If anyone thinks of anything else - please add the this post!
Thanks
Jim
I posted it years ago - but a rough idle brought it up in my mind so I am re-posting it - hopefully it will save someone some work. This isn't everything - just some common answers to common problems. I don't get into Needles or re-jetting here - just getting the bike to run smooth.
I have an 81 with 34's:
135 MJ - 135 Airjets
45 idle jets
John's needles - Canadian jets.
Runs GREAT!
I have a set of stock 34mm for my 81 Heritage 650 special - and for kicks a bought a second pair - for back up and to experiment with.
Here are some tricks to some problems I ran into that helped me –
Start with Problems –
Rough Idle?
Look at Spark Plugs - Are Plugs Wet? If Yes Look at Floats / Needle Valve First.
Are Plugs Dry? Look for Air Leak near Carbs – OR Clogged Pilot Jet Passage – Or Incorrect Fuel / Air Mix.
(Try this first – Get some Good Carb Cleaner – Spray Type – and put the "straw"into the Pilot Jet opening and the Main Jet Opening One at a time and blast the passage.) (They are located on the air filter side of the Carb at the throat opening– round holes at 4 and 8 O'clock. )
Here are some Other tips that helped me...
Tips for beginners.
1 - get a book
2 --do one carb at a time -
3- view just about evey post in the fuel sections for tips.
To set idle air – fuel mix
Carbs mix air and gas - as I recall the perfect mixture is 14 to 1.
Too lean (too much air) causes hesitation, knocking, poor idle and heat -
Too rich (too much gas) causes plug fouling, backfire.
As a general rule with any carb - gently screw the idle mixture screw in until seated counting the turns clockwise. WRITE IT DOWN>
Then unscrew the screw to that point or 1.5 turns.
Start the engine - slowly 1/4 turn at a time screw in until the engine rpm drops - this is lean roll off - note the turns in. Now unscrew past optimum idle until the rpm drop from too much fuel - this is rich roll off - again note the turns out - Mix should be set dead center of these 2 figures --- for example -
Lean roll off 1
rich roll off 3
Ideal is 2
Rebuilding:
So far what I have seen here is that - if it has an O ring replace it.
foam floats like a float level of about 22-24mm - but it varies from carb to carb. The yamaha manual has lots of information about the carbs - you can get it free here
www.biker.net/650parts_index.html
Notice the section on checking the float level with a clear tube (done on bike)
Take a clear tube and attach it to the drain nipple on the bowl of the 34 carbs with the bike LEVEL! Loop the tub up the side of the carb like a big J. Put the fuel petcock on PRIME and open the drain screw on the carb bowl. Fuel will flow up the tube. If floats are correct the fuel should stop at the top of the bowl right below (1-2mm) the seam between the bowl and the carb body.
DON'T MESS WITH THE FLOATS -- IF THEY ARE WORKING.
Concentrate on cleaning the Jets and passage ways.
Check the diaphrams - for tears (see below)
remove all the jets and clean them with compressed air - check passages by viewing light through the holes.
Be gentle! Brass bends easily.
Other Helpful stuff...
1- floats - judging by the condtion of the float pins in both sets - I can see that people have trouble removing pins that have been in for a while - simple solution - use a fine drill bit the slightly smaller than the diameter of the pin - and gently tap out the old pin using the drill bit as a "drift." I mount my carbs sideways in a vise (clamping on the angle iron that joins the two carbs) line the drill bit up with the end of the pin opposite the T and tap the drill bit lightly until the pin is pushed out. The smaller drill bit then easily pulls back out through the hinge.
One more note:
I discovered that the replacement foam floats from MIKES actually bind in the float bowl - not good. Hinge is loose on the pin.
I love mikes to buy stuff - but if you use these floats - they will require modification.
A small brass tube from a hobby shop works well to shim up the difference between the floats hinge and the stock pin.
2- float levels – Buy a micrometer at harbor freight for $20 it's a must for carbs.
on 34mm - the factory float setting of 27mm is just WRONG. 22-24mm with no gasket is dead on. Also when comparing both float levels - check them both at rest (normal) not compressed - both sides should be equal (height while depressed doesn't matter as long as they are equal). Bending the tang to adjust the floats can effect the level of the how evenly they close - so they may match at rest - but don't match at operation.
3) Bench testing floats - mount your carbs in a vise (as per above -by angle iron between carbs) Use a level to make sure they are level at rest.
Take your 2 gallon lawn mower gas can and set it on a shelf higher than the carbs. Run a 1/4 siphon tube from the gas can to the carb gas intake and let them fill (siphon action from can to carbs)
Attach a clear tube to the drain nipple on the bowl, and open the drain screw - hold the clear tube up to the edge of the bowl (it will now be U shaped) and compare the gas level to the side of the bowl - repeat for both carbs - both gas levels should rise to about 1mm below the TOP edge of the float bowl - AND both sides should be equal. This save the trouble of mounting and removing the carbs - each time you need to adjust the float levels.
4) Diaphrams - Close the Choke! Put your thumb over the large opening on the top of the AIR cleaner side of the carb - push the diaphram / needle assembly in the throat of the carb UP - and release it while keepin the hole covered. The assembly should hold in place or fall VERY slowly - if not - you have a leak.
5) Float hinge - make sure the brass insert is in the float hinge - many aftermarket ones are missing the insert and cause the floats to ride floppy on the pin - re-use the old insert - or fashion a new one from brass tubing from a hobby store to clean up the action.
6) Idle mixture screw O ring - After removing the brass plug - and counting the factory number of turns until the needle is gently seated - your should remove the needle for cleaning. Often it leaves the O ring and washer still in the hole. Use a small paper clip - with the end bent into a J to gently fish out the old O ring and washer.
If anyone thinks of anything else - please add the this post!
Thanks
Jim
