Possible fuel line issue?

[oldyam80sg]

I have a 1979 XS1100 special. I hardtailed the rear and made a chopper out of it and put a harley tank on it. I have pods and custom 4 tube exhaust with no mufflers. I had Sigma get a jet kit for me and I installed it. I also put in new diaphragms and the bike still isn't running right. I currently have a on/off/RES petcock on it (not factory) into a 1/4" hose into a T into two 1/4" fuel lines and then into the carbs. Could it be the way I have the fuel lines running? I bought a Y to try, but I figured I would ask here first to see if anyone has run into this before. Do I need a different pitcock? Two petcocks into two fuel lines? I really don't want to do that, because I have a sick paint job on the tank. At times, like twice run pretty good so not sure if the fuel lines get air in them or don't flow very well. Here is a pic of the tank. You can see the petcock down on the left side. I will try and upload some pics of the fuel line situation tonight. I gotta think some of you have run different tanks and have a fix. Please help. So close to having this project ready to ride.

Looking at this pic-where is the vacuum cap? Bike will run like crap with this missing.

[oldyam80sg]

Starts ok. Idles pretty good. Then it doesn't take throttle well and won't rev well.

Be aware that my very own "usual" XS1100 Starts and runs well on full choke. Then I switch to half choke for about 3 miles before it's up to operating temp so's it can idle/run right and I turn the choke OFF to ride around all normal like, again...takes about 3-4 miles of running on half-choke to get to the proper temp to run right without choke. ໒(⊙ᴗ⊙)७

WITHOUT the choke and BEFORE that 4-5 miles? (O_o)

GUTLESS as a Ford Pinto runnin' on 2 cylinders. (－‸ ლ)

TLDR version- Idling in the garage ain't NEVER gonna get yur XS up to temp so's it'll pull/rev like it's s'posed to. (O_O)

Seems like pipes are heating up pretty similar. I can do a better check on that.

Iffin' you don't got's an Digital IR Thermometer? (O_o)

THANK YOU. They's mostily made in China using stolen patents. (●´⌓`●)

Don't EVER touch those pipes wit' yur fingers. Use a water bottle to spray'em and watch to see how fast the mist boils/flashes off. OR NOT in the case where's one pipe/cylinder ain't playin' well wit' they others. ( ´ Д `)ﾉ

Original carbs, I assume the vents lines are the ports just to the right of my index finger in the 2nd pic. Open and no hoses on them.

Correct. (^_^)

Usual to put some kinda short line wit'a filter on'em but that's down the road a ways? (O_o)

It doesn't seem like it acts like the video from above.


That's GOOD. (^_^)

Mainly cuz the reason so many bikes run like the one in the video is due to cheap Taiwan Carb kits with bad needle/seats fOaR the floats. You set the floats to the right height like yur s'posed to yet the fuel levels in the bowlz are WAAAY off and usually so high the gas is just splattering in thru all the orifices in drops/splatters instead'a a fine MIST in the correct right ratio. (☉_☉)

Some of the "symptoms" when jets from the the Taiwan Kits be installed? (O_o)

1. WON'T start w/o cracking the throttle to give mOaR air. Leave the throttle closed and you'll crank till the battery just DIES. (*′☉.̫☉)

2. After 2 minutes of warm-up/idleing in the driveway you CAN turn the choke completely off and drive away all normal like. But that's only because the Taiwan jets are so RICH it's as if you NEVER turn the choke off anyways.... (－‸ ლ)

3. At around 5-7 miles of actually riding and when trully at operating temp? (O_o)

Below 4k rpm, twist the throttle a bit and it'll NOT accelerate. It'll try to STAY at the speed you are or even SLOW DOWN/BOG. ( ˶⚈Ɛ⚈˵)

4. Cut the throttle too quickly at 4k rpm or above? (O_o)


p-p-p-p-Buh-OOOM! As in much more than an annoying popping out the exhaust. A REAL ASPLOSION which iffin' you got's slide-on/clamp mufflers will blow'em off iffin' the clamps an't tight. ┐('д')┌


You SURE that the lips of the pod filter(s) ain't fully or partially obstructing any of the CRITICAL air holes around the outside of the carb inlet bell? (O_o)

My suggestion is to go fer a ride. 1/2 choke for about three miles then choke OFF.

Might be this simple. (O_o)

Larry I think personally you are leaving the choke on too long-3 miles and then half choke? Takes me usually about mere minutes before I go half choke and the maybe 30 seconds before choke is pushed all the way in. My plugs are nice and have a slightly tan color. OP should look at what the plugs look like. Are the carbs cleaned? Remember no carb cleaner in the bottle will help if other things are dirty. And then are the carbs even synced? What pilot and main jets are in the bike?

[Larrym]

Larry I think personally you are leaving the choke on too long-3 miles and then half choke? Takes me usually about mere minutes before I go half choke and the maybe 30 seconds before choke is pushed all the way in. My plugs are nice and have a slightly tan color.

Larry I think personally you are leaving the choke on too long-3 miles and then half choke?

Full choke is used only to start and then mebbe 30 seconds later I go to half choke and drive away. (･‿･)

I DON'T ride/drive wit' full choke on....ever. ( •_•)

Bike had OEM/Mikuni jets when I first got it YEARS ago and that's just how it ran. NEEDED half-choke and minimum of 3 miles riding before it got to operating temp so's I could turn the choke completely OFF and engine ran/idled properly. 彡໒(⊙ᴗ⊙)७彡

The "Tell-Tale" fOaR when to turn the choke completely off was/is when I come to a stop and the engine is idleing FAST. Turn the choke off totally and then it idles at the prescribed 1000-1100 rpms. (^_^)

BUT when I bought/installed the Taiwan carb kit/jets? (O_o)

After I fixed the fuel level problem I ran it fOaR less than 20 miles wit' the Taiwan jets installed. (－‸ ლ)

Symptoms are detailed in the post you quoted. Mebbe something fOaR others to look at to explain why their bike ain't running like a super bike... ┐(´ー｀)┌

Bike NOW has OEM/Mikuni jets and it's running just like it did when I first got it and fixed the ignition problem. GREAT! (^_^)

Takes me usually about mere minutes before I go half choke and the maybe 30 seconds before choke is pushed all the way in.

THAT is the symptom I got when I had the Taiwan Jets installed...plus it wouldn't start w/o cracking the throttle to give it more air. Ran strong even when cold and NO CHOKE but was totally LAME when it finally got up to operating temp. (´～｀)

It was like riding an XS850 instead of an XS1100. (￣ヘ￣)

That's me...but IIRC, didn't you have someone go thru yur carbs and put in some aftermarket jets/needles? (⊙_ʖ⊙)

[oldyam80sg]

Never had anyone except me go through this bike and touch the carbs since about 1986 . I have had my XS since 1986 so I think I know a thing or 2 about these bikes. I do have a Dynojet recalibration kit installed in 1986 by a Yamaha mechanic and the jets are Genuine Mikuni. There are no shops by me that will look at a bike this old. I have done the work myself with help from this forum.

[oldyam80sg]

Shopteach-are the carbs cleaned? Are they synced? What do your spark plugs look like after a ride?

[DEEBS11]

Just a note on Dynojet kits. They are a proprietary jet kit. In other words, the Dynojet company makes it's own (quality) jets. They have a proprietary jet number that does not correspond to Mikuni or Keihin carb. This makes it very difficult for the future mechanic to figure out years down the road when they are trying to figure out what jets they have if they don't know what they are looking at. The tell tale sign is in the adjustable needle but even then some bikes made before 79 have adjustable needles stock from the factory. This causes many problems and many new owners of bikes end up here or some other forum looking for help that will never come because of the unknown modification. This is also true with Chinese junk jets that are apparently drilled with masonry bits. Too many modifications. Too much complication. Many, many opportunities for problems.

[Larrym]

I do have a Dynojet recalibration kit installed in 1986 by a Yamaha mechanic and the jets are Genuine Mikuni.

I do have a Dynojet recalibration kit installed in 1986 by a Yamaha mechanic and the jets are Genuine Mikuni.

Yup! That's wut I wuz remembering from years ago...Alls I had to do was read it in yur signature. (｡•́︿•̀｡)

DYNO-jet...and Genuine Mikuni Jets installed at the same time? Wowzers! ┐(°ヮ°)┌

Might explain how's come you can just turn the choke completely off after 30 seconds of idling in the driveway and ride away all normal like. (O_o)

Comparision of Apple and oranges here as I've only had direct experience wit' wut happens when someone (me....) with a stock bike/carbs buys and installs the Taiwan Kits offered on Fleabay.... THEN swaps back to genuine Mikuni in order to get the bike to run like it did beFoAr the kit wuz installed cuz it ran so badly.... ¯\_(シ)_/¯

IIRC, the OP don't got jets/needles like EITHER of us. Some kinda kit frum SIGMA? ¯\_(°╭╮°)_/¯

I gots absolutely NO experience or knowlwdge 'bout THEM or how's they's s'posed to wurky.... (ノ_<。)

[oldyam80sg]

Heard very little from Sigma.

[shopteach]

Sorry guys, I've been really busy. I finally got some time to work on it and I ran the bike as best I could by myself (one hand on half throttle, and the other playing with the wires) and I couldn't get anything to change. So I thought I would try and check the system from the ignition coils to the P/U coils. I tested the ignition coil as per manual and I got resistance between the primary side (little wires), but none on the secondary side (plug wire side). The coils wires are very hard and seem brittle. My thought is that the coils wires aren't good and made contact at certain times and not most of the time. Thoughts there? Does anyone have suggestions on where to get a coil? Places to stay away from on getting a coil?

oldyam80sg asked about the vacuum cap. My thought was it was this or is it this? Or am I completely off base? If it is different than these could you send a pic so I can address it?

You also asked about the carb being clean and yes they are. Synced, I haven't because I am trying to limit adjustments until I get it running better. I figure it should be at least close and don't want to throw one more variable into the equation, I already have too many at this point. And I haven't been able to run it enough to check the plugs.

[DEEBS11]

This is a good start. There are forum topics on how to install in the search function.

https://www.ebay.com/itm/365386060271?_skw=dyna+3+ohm+coil&epid=654218986&itmmeta=01JW8GV4M2DAK8HZYAYZSKX0F1&hash=item5512b4d1ef:g:eCgAAOSwkC5np4Ez&itmprp=enc%3AAQAKAAAA8FkggFvd1GGDu0w3yXCmi1ff76AfVa3NZ1%2BpvMLs3xRQSnOjTZ6r1QoN3PFwpVPPFRNpIRkuYC7fYjtllBpdsA%2F****h80AxHX6o60%2BGD1iUM7tI%2Ff%2FpYW1s2KvN56E7zbGRpBeDK80yyc6SebtUmMnpn%2FSVglgylr%2FFQ30sAr7jlVvsGAx%2B6wg%2FcRMhvW%2BfVIGG7pWylqJ1juMahwaYgp2JYUtdCJEwyB5mknRnt6HQspj%2FsXgLTBQMvQYL4g%2B3ql36gugPxwo3IDZubHpLAFRjFHYWfZ2iUYdW46UEqmT9AF2ZZ4K7Hs1FxheRvvtDSg%3D%3D%7Ctkp%3ABk9SR6LK7JDiZQ

[DEEBS11]

But to NOT buy this Chinese garbage copy.

https://www.ebay.com/itm/314295443836?_trkparms=amclksrc%3DITM%26aid%3D1110006%26algo%3DHOMESPLICE.SIM%26ao%3D1%26asc%3D264183%26meid%3D3225254971c84adf88b6f75d820edae4%26pid%3D101875%26rk%3D1%26rkt%3D4%26sd%3D365386060271%26itm%3D314295443836%26pmt%3D1%26noa%3D1%26pg%3D2332490%26algv%3DSimVIDwebV3WithCPCExpansionEmbeddingSearchQuerySemanticBroadMatchSingularityRecallReplaceKnnV4WithVectorDbNsOptHotPlRecallCIICentroidCoviewCPCAuto%26brand%3DOE%252B&_trksid=p2332490.c101875.m1851&itmprp=cksum%3A3142954438363225254971c84adf88b6f75d820edae4%7Cenc%3AAQAKAAABUG96wQ16jds4VFcrhy1F3d4mbwZUJI9Fs%252BgdXYAHIzlX2e3YaNh7x%252BEnKA3G%252BCqSl1Xn4McfcWFK1GytmS2qxJ87mtE8Gm3iR1Ja4WBwh0hNHJrJx3Ki5mp04ow4CO7lP%252BooCybZDDU%252BbbSwmg7CbTin%252BBzBzbCYVnbjvyQAHu6--HI4MB7SvJl5IJqlyvomgoLMlgT6qAJzX0SANJhty2eflQEVL2kQtii9BwsJAPWgVbkQ9x%252BuyIqEYXwDDgp4KfW2BqjN5SoUJGKae9qz7QRn%252F1wQrydFCQiKe%252Fnqtx6sNL48jiQjhW1ramz5puJOHCImnc%252BV5GhDx9LQfw7pu4ItlQRhws%252FfxjG5ggQ5KUxsk6PGCvSZby7R9emtwl%252BNJYGqdlhx1WBeKzNlPOA5Ybmky7vG4T8ARMJ6QaamPAUHBDocOJWoWKbOTblNJBzvpg%253D%253D%7Campid%3APLP_CLK%7Cclp%3A2332490&itmmeta=01JW8H19HM8EKX7TY9EMP7SA9X

[Larrym]

No wurries or hurries on this side of the interweb... (^_^)

The foist pic showing the Vac port on the intake boot between the carb(s) and the engine covered wit' a female black plug lookey just fine. (´ ᴗ｀)

Iffin theres a plug missing or even slightly cracked (and a vacuum leak...) at any of the 4 (four) caps then you'd be surprized at how crappy these engines will run. (◕_ゝ ◕)

[oldyam80sg]

Shopteach- use the search button on here and do the bread tie sync-that will get you close-I have used it on older bikes others than ours and had success. Yes vacuum cap in your 1st pic is the one-You should see some more -they become cracked and dry rotted and need to be replaced. The bike will pop if they are bad and not run good.

[DiverRay]

Looking at the photos I see one thing no one has mentioned. The fuel lines are connected to the bottom "T" fittings between the carb 1,2 and 3,4. The top "T" fittings WERE connected to the airbox, as vents for the carbs. If something crawled in and died, no vent, no happy carb. You need to make sure the vents are clear, and then put a small filter on each one. A paper "fuel" filter will work.

[oldyam80sg]

Good eye Ray! I looked at pics of my carbs and had a brain lapse and couldn't see what was different.