Still Not Working Right!

[Jacobite]

To refresh your memories I have a 1981 Special that had no power until it went over 3000 rpm. (To borrow another posters words it was "bogging down"). I figured the problem was in the carbs, so I cleaned and recleaned - adjusted the floats, set the idle screws, bencehd synched it - still no change. I finally got fed up and went to the local dealer. Their mechanic said I needed new floats (@$23 each) and new needle valves (@$53 each). I thought - well I've tried everything else - and they said it should run like new after the fix. Well, several weeks later - and with my pocket $440 lighter - it still isn't working the way it should. When I start the bike, the symptoms are all still there. It has no power until it hits 3000 rpm and then takes off. I talked to the mechanic who said he test drove it and once it was good and hot it worked perfect. He said I had put 20/40 oil in it and it really needed to heat up good to work right (the day I picked it up it was about 90 degrees out - !!!???) - he said he couldn't "tune" it for hot and cold so he "tuned" it for hot (!!??). I have driven many bikes, an they all warmed up within ten minutes. After I drove mine for a half hour or so, he was right, it does work good - pulls hard from a stop right through the rpm range.

It still is brutally hard on fuel - about 60 - 65 miles to a tank of fuel. When I called the mechanic, he said we should do a compression test (I never have). I have gotten some ideas from some recent posts about bikes with the same symptoms - any ideas about why it would work better when hot? I know a piston will expand a bit when it heats up - could a valve do the same thing? A compression test will tell me if I have a ring or valve problem. I don't know anything about the vacuum advance - is there anything there that might change with temperature?

Any comments will be appreciated. I need to expand my range - or build an auxilliary gas tank!

[randy]

Jacobite,

What you describe is a very rich running engine. Pull the plugs and take a read. I'll bet they're black, which would confirm rich mixture. Do you know if any jetting work had been done previous to this problem? And, did this "mechanic" fool with the idle mixture screws attempting to "tune it for hot"? You may also have clogged jets elswhere in the carbs, that he is not familiar with and may have overlooked.

Lastly, don't go back to that shop. You bike was probably manufactured before that "mechanic" was a gleam in his fathers' eye! There are very few people left around, nevermind still working at dealerships, that can properly tune an XS. If you're ok with wrenches, keep plugging away at us here on the forum and I'm confident that you can work through your problem. It worked for me.

HTH

Randy

[Geezer]

If you put in new pilot jets, that may be your problem. Somewhere along the line the design of the pilot jets changed and if you're not paying close attention, the new ones don't look all that different.

The new style jets cause the bike to run rich but around 3k or so RPM you are running on the main jets.

Geezer

[JohnSg]

Sounds like the pilot jets or air jets may still be plugged.

[sidecarKev]

The best thing to do is work on it yourself. All the members here can probably tell you how to do it much better than most bike mechanics today. (hopin' I'm not pi$$in off any of them, I guess if there on here they aren't like most)

There is nothing in those carbs you cant accomplish with the help of a thousand or more other owners.

Just for example, and I'm not trying to sound like a jerk or anything but you could have purchased the floats for $10 each and the needle valves and seats for $10 a set. So total parts would be $80.
The hardest thing about doing carbs is getting them in and out. And I hate to say it but they have to come out again. I agree with JohnSg, the pilot jets or air jets are clogged. I had the same thing on mine. I had been clening my carbs but everytime I had been skipping the pilot jet under a screw in my carb. Finally I figured out what was going on and I cleaned those jets. Sure enough 2 were clogged. After that I had much better throttle reponse.

[Jacobite]

Thanks very much for the responses. I had read on here before NOT to take the bike in to the shop - but I was getting frustrated, it is a hard way to learn a lesson. Never again.
I hate the thought of taking the carbs out again (actually it is putting them back in that is the real pain), but I will - and this time I will ensure there is no crevice that has gone unchecked.

The dealership checked on the needle valves & seats & said they couldn't source them aftermarket - so those prices were for OEM. I though it was ridiculous, but if had worked I wouldn't be complaining.

Nothing has been done to the jets since I've owned the bike - and I doubt anything was done previously.

Where are the pilot jets & air jets?

Thanks again,

John

[sidecarKev]

Best view I've seen for pilot jets without actually seeing them on the carb is here.


I think this is linked to another members site.Carb Diagram

Pictures of the jets can be seen here.
Carb FAQ

[randy]

Jacobite,

The pilot jets are located under the float bowl next to the main jet. When you remove the bowl, the main jet is visible in the center of the works. It's brass with a slot and a hole in it. Right next to that you'll have either a slotted screw or a rubber plug. remove the screw (or plug) and the pilot jet is screwed into that well. Use a good light down there and you'll see the slot. it's a good 1/2" down there.

The pilot air jet is located at the carb throat where the air box connects. Looking at the throat, there are two brass inserts, IIRC, one at 2o'clock and one at 10 o'clock. These passges are connected inside the carb and run through to the mixture screw jet that is next to the manifold. the sequence is:

Pilot Air Jet ...to...Pilot Jet...to...Mixture Screw Clean them trough From Pilkot air to Pilot and then Pilot to Mixture with a spray of carb cleaner so it sqiurts out the other side. that should do it. Before you replace the jets, clean them too.

Set your mixture screws at a base setting of 1-1/4 turns out from a gentle seating. She should run pretty good after this. Then you can gradually adjust the mixture if you have stumbles off idle or if she pops in the exhaust, turn the mixture screws out 1/2 turn each at a time and then test ride again. You'll know when it's right.

If this doesn't cure the problem, you may need to take a look under your pickup cover. More on that later. Keep us posted.

Randy

[sidecarKev]

Word of caution on removing the jets. They can be kinda stubborn to get out so make sure you use tha correct size screwdriver to reduce the chance of messing up the jets.

[Winterhawk]

Sounds to me like you used K+L's pilot jets. USE ONLY OEM on these or it will never run right. Even K+L's needles and seats are trash, use OEM needles and seats also as K+L's will NOT seat properly.

[skids]

I just have to draw a better diagram! I think I disagree about a previous comment concerning the pilot circuit running too rich. When an engine is cold the vaporization of the fuel is not as efficient, so they usually need the enrichment circuit (choke). If the bike is running better after warming up, is is probably a bit too lean. I can't tell you if the pilot screws need backed out a just a little or if the pilot jets need to be a bit larger, of if the float level is too low...all could affect low to middle rpm range. The adjustments should be made when the engine reaches normal operating temperature, however.

Originally posted by sidecarKev
Best view I've seen for pilot jets without actually seeing them on the carb is here.


I think this is linked to another members site.Carb Diagram

Pictures of the jets can be seen here.
Carb FAQ

[ratbyk]

skids, if he is only getting 60 miles to a tank of fuel it is definitely to rich. (of course if it is a Special-that is to be expected)Tee Hee
Ken/Sooke

[Jacobite]

Thanks very much again for the suggestions and tips. Now I know what my plans are for the weekend! I do think the bike is running rich - the plugs are black & the gas mileage is brutal (which is really bad with the specials mini-tank!)

All the parts I've used are OEM, and the problems were there before the new parts, so I don't think they affected anything

Thanks fro pointing me to the diagrams etc. Looking at them, I'm confident I cleaned the air jets. I'm not so confident I cleaned the pilot jets - so I'm thinking they are the culprits.

I'll let you know how I make out.

Thanks again.

[DEmily]

I experienced the K&L pilots myself and it is true that they do cause issues. Have you made any chages to the stock exhaust or air filter? What color are the plugs after you ride?

[Jacobite]

No changes to the exhaust - only change to the air filter was to install a new one (stock).

Plugs are black after I ride.