Author Topic: Carburetor rejetting question  (Read 6486 times)

frappy

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Carburetor rejetting question
« on: August 30, 2014, 01:35:02 am »
Just purchased a new-to-me ’82 FT500 with 3,300 miles on it.  Entire bike including engine and exhaust are bone stock.  It seems a little hard to start and feels a bit underpowered when riding down the road.  However it runs smooth if I ride away with the choke on when cold, and will idle fine once the engine’s warmed up. I am keeping this bike on a trickle charger and the battery is showing xx.x volts across the battery terminal at idle.

Maybe it’s just me being picky, or not knowing the exact starting sequence.  However, it did not start the first time for the PO as well, and I am wondering if that is a symptom of simply the carb needing to be rejetted, or if there are other issues.  The bike eventually comes to life, but maybe after 3-4 revolutions of the starter when the engine is cold or has been sitting awhile.

I would like my engine to come to life on the first or second revolution of the Ascot’s fragile starter motor, but it doesn’t.  Maybe I just need to learn the starting routine, but after reading the “Ascot essentials” article, I went ahead and ordered the 2x oversize jets from Mark at Thumper Stuff, in hopes of getting my bike to fire and hold idle a bit more quickly.  I could just go ahead and install the jets, but am kinda’ curious before I do as to what are the specific advantages of the upgrade.

For instance, once I install the new jets and a new float bowl gasket, will my FT500 start more easily when cold?  Will it need less choke?  How well will  it start when warm?  Will it have better performance off idle, at certain RPMs, or everywhere in the power-band?  Lastly, are there any other adjustments I need to make to the carb once I install the up-sized jets? 

In the long run, I am hoping that the new and bigger jets will help my bike to start a little easier, perform better, and relieve some of the stress on my starter motor. Thanks again folks for your feedback.
 

FT500R

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Re: Carburetor rejetting question
« Reply #1 on: August 30, 2014, 09:33:57 am »
What really helps for me is to open up the throttle twice before starting the bike. It usually fires right up even without the choke.

This is with the standard jetting.

J6G1Z

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Re: Carburetor rejetting question
« Reply #2 on: August 30, 2014, 10:15:45 am »
The new jets will help cold starting somewhat, but mostly they resolve the lean burn condition that exists in OEM configuration. The new jets will provide a bit more power & allow you to add one or two teeth to the countershaft sprocket. I chose to upgrade to a 16 tooth countershaft. Stock is a 15 tooth. The larger countershaft sprocket allows the engine to operate at a lower RPM range.

There is a starting procedure that you can use to help the starter. Remember that the carb has an accelerator pump. This is a very nice feature. The accelerator pump squirts a fine stream of raw fuel into the carbs intake tract when you rotate the throttle. This is to prevent the engines tendency to hesitate when the throttle is whacked open. Use this feature to your advantage when starting. I usually rotate the throttle about 3-4 times to prime the carb. Plus I use the full choke when the engine is cold. Make sure you push the start button right in the center & hold it down firmly while starting. Of course you need to let off as soon as it fires. I have a few Ascots & they are all cold blooded. I usually let the engine warm until the cylinder is warm/hot to the touch. Even then I usually need 1/2 choke till I ride to the end of the block. Use that choke as much as required & don't be concerned with it. Before starting, remember to prime the carb by pumping the throttle 3-4 times & see if that doesn't help.

Good luck
J.

frappy

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Re: Carburetor rejetting question
« Reply #3 on: September 08, 2014, 02:33:41 am »
So, I've pulled my FT500 float bowl and jets.  The existing stock jets I removed from my carb are Pilot Jet 52 and Main Jet 140.  They are both marked as Keihin jets.  The jets I got from Thumper Stuff are Pilot Jet 58 and Main Jet 145.  Are these new oversize jets going to create a problem?  My FT500 is bone stock California bike.  I thought we were supposed to go two (2) sizes bigger?  Will the +6 Pilot Jet and +5 Main Jet work, or do I need to get smaller "oversize" jets?  Any info/guidance from more experienced Forum members would be most appreciated.  Thanks!~

J6G1Z

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Re: Carburetor rejetting question
« Reply #4 on: September 08, 2014, 08:32:34 am »
You have the correct jets. Keihin jets are numbered oddly.

Did you have any trouble removing the low speed jet? I almost stripped the slot out of mine.


J.

frappy

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Re: Carburetor rejetting question
« Reply #5 on: September 08, 2014, 09:10:24 am »
Thanks.  Nope, I used a vice grip on the shaft of a "shorty" flat blade screwdriver.

frappy

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Re: Carburetor rejetting question
« Reply #6 on: September 09, 2014, 05:18:40 am »
Got the jets installed in my FT500 last night and (thanks to J's recommendation) didn't even need to remove the carb.  I also decided not to replace the float bowl gasket and thankfully it doesn't leak after reassembly and testing. Maybe I should've ridden the bike more than once before I changed to the recommended 2x oversize jets, but I'm not looking back.  The bike seems to start, come off choke, idle, and just plain run better throughout the rev-range.

To attack the job, I removed my side covers, seat and tank.  I loosed the clamps on the rubber intake and air box clamps to allow me to twist the carb as needed to get out float bowl screws, remove float bowl, and remove/replace jets.  I also removed the 10mm head bolt on the breather (Honda's fiche calls it a "storage tank") to permit me to move it around when I needed to drop the float bowl (see pic).  Before dropping the float bowl, I made note of the position of the enrichment set-screw lever on bottom of carb (in front of bowl).  I employed a couple of make-shift tools to remove (and later reinstall) the float bowl screws and two jets. I used a screwdriver bit and either a 1/4" socket/ratchet or box-end wrench to remove the bowl screws (see pic).  The Main Jet came out easily with a 7mm (or 8mm) box-end wrench, and for the Pilot Jet I used a shorty screwdriver clamped very securely in a small Vice-Grip pliers (see pic). Once the old jets were out and new ones installed, I reattached everthing in reverse order then moved the carb back to horizontal and aligned notch on boot to corresponding tab on side of carb (see pic). 

Here's the pics of the tools I used to replace my Main and Pilot jets, the breather I loosened and the carb alignment notch. Hint: you will need to apply significant upward pressure on the driver bit and also the small shorty screwdriver, in order to avoid stripping the float bowl screws and pilot jet. I needed a small mirror to see and locate the slot position of the Pilot Jet, I did also need a flexible magnet to recover a float bowl screw when I mistakenly dropped it on the engine.
« Last Edit: September 09, 2014, 05:27:07 am by frappy »

J6G1Z

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Re: Carburetor rejetting question
« Reply #7 on: September 09, 2014, 10:28:37 am »
Good job! Thanks for the write-up & pics. This will help other folks that come along later.

One of those float bowl screws is a bit difficult to get to. To remove the slow speed jet, I used a parallel ground gunsmith screwdriver that fit the slot perfectly. I first tried it with a regular screwdriver & almost stripped out the notch.

Another great & simple modification that really helps after the jetting change, is to swap the countershaft sprocket to one or two teeth larger. The OEM stock countershaft sprocket is a 15 tooth. I swapped to a 16 tooth & really liked how it allowed the engine to lope along at highway speeds. Some guys go with a 17 tooth, but on some bikes there is a washer that needs to be clearanced for the 17 to fit.

Modify the bike to build more power, than gear it up to go faster.

J.

WTF304

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Re: Carburetor rejetting question
« Reply #8 on: December 29, 2014, 07:48:35 pm »
Hello guys, I'm new to the forum but not new to this bike. I forget who posted the dyno pull but reading it gave me a little insight on re jetting mine. Have the manual infront of me ( after digging it from my shelf)  and was curious to know something. Now assuming the slow jet ( pilot), is different size depending on where the bike was sold ( again, assuming that basing an opinion on altitude) because the book doesn't really say it's factory/generic size. And i think but could be wrong but i recal somewhere it was listed as a #35, i had one that was setup to ice race and the slow jet was a #52. The main was still a 140 like the book said and i haven't pulled the carb from my stock FT to know if it has been opened up. Is the factory installed jet a #35 ? Or was that just some bs i read ? .... i went to my somewhat local shop today and picked up a #52 slow jet and a #160 main in hopes to fatten up the fuel mix a bit, don't want to run lean. My ice race bike was put together by the PO and that was years ago when i bought it off his hands.

WTF304

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Re: Carburetor rejetting question
« Reply #9 on: December 29, 2014, 08:08:00 pm »
Nvm guys i did manage to find the size spec for the slow jet in the book, it's been awhile ( laughing at myself ) for some reason i didn't think it was stock. ;D