Gas consumption is way too HIGH, Mileage too low

[RichV]

SO....if I were you knowing what I know now, I would probably put in 115 mains but stay with the 42.5 pilots with your setup. The N100.604 is the right number for the MAINS...but can't find a reference to match the 2nd number....but the PILOT is the BS30/96 type/style.

Thanks T.C., I think my number was wrong for the pilots. Once I test the coils better I'll order the jets.

How many miles on the carbs ?
Could be worn emulsion tubes/main needle seats ?
I was getting 30 and thought that bad but your mpg. is washing your pistons and cylinders dry !!!!!/ or where is that fuel going, in the air cleaners or on the ground ?
How many miles have you put on it ?
Do a real test, fill it, put miles on it fill it, see what it's using, could get real scientific and use a dip stick to make sure your filling it to the same level. Not to full though, hate getting fuel all over my paint.

The carbs are cleaned rebuilds with about 100 miles so far. The mileage is more like 20MPG after I measured it a little better yesterday.

There are no current leaks. I did have a problem with 1 and 4 floats sticking after the rebuild which I fixed. The would both leak during a static leak test.

[RichV]

I found that the plug cap on #3 was reading .4M ohms. Swapped it out the bike ran better for a while. Eventually, it started again so I may have thermal breakdown in the coil.

or.. the cleaned plugs just got fouled again after a few miles.

I'll swap out the coils when I get a chance to see if there is a impact.

Meanwhile, I'll order the replacement jets per TC's suggestion.

All four coils I have read the same on primary (2,6 ohms) and secondary (12K ohms). Caps were different on the installed coils.

#1 - 7.73K
#2 - 5K
#3 - .4M (yes meg)
#4 - 7.48K

I swapped the #3 with a 5K on the backup coils for the test.

The other caps on the backups coils were around 10K each. Looks like the caps are burning out and need replacing.

So it looks like I'll be ordering the caps as well. Anyone have a source?

[TopCatGr58]

Hey Rich,

You can get caps from Dennis Kirk also, so you can save some $ on shipping by bundling your order items! There is a guide in the tech tips on what description letters/numbers combo you need to look up if you want to retain the exact same shape/size....like longer reach, 45 degree angle for the inner 2 vs. the shorter reach/90 degree angle for the outer 2. Also, you don't really NEED the resistor caps. The spark plugs are probably already resistor because it's more difficult to find non-resistor plugs anymore.

Also, you can take the plug caps apart. Unscrew it from the plug end, take out the inner resistor, spring, clean and check the resistance value. IF it's still HIGH after cleaning, then the resistor is damaged, and you do need to replace the cap.

T.C.

[RichV]

Thanks T.C.

I ordered four caps at the same time. All of the are 5K resistance. They only had the short ones and the 45 degree ones so I may take the resistor out of the new ones and put them in the older, longer caps.

I will take one apart tomorrow and look at cleaning them up.

[MPittma100]

Resistance

Thanks T.C.

I ordered four caps at the same time. All of the are 5K resistance. They only had the short ones and the 45 degree ones so I may take the resistor out of the new ones and put them in the older, longer caps.

I will take one apart tomorrow and look at cleaning them up.

Resistors in the plug caps are engineered to do one thing only (same with resistor plugs) - reduce radio interference RFI (noise). Engine performance is unchanged with or without resistors. You can make a metal "slug" and put it in place of the resistors. Some of the end caps do not come apart.

[RichV]

Resistors in the plug caps are engineered to do one thing only (same with resistor plugs) - reduce radio interference RFI (noise). Engine performance is unchanged with or without resistors. You can make a metal "slug" and put it in place of the resistors. Some of the end caps do not come apart.

All the caps I have come apart. I plan to leave the 5K ohm resistor in because of the interference issue. Hopefully the ones I ordered do come apart so I can swap the resistor. The were not that expensive.

[RichV]

T.C. (or anyone else)

My vacuum advance is not operating as I would expect. I was under the impression that it's supposed to engage when accelerating. Nine engages while at idle causing the RPMs to rise about 1K. Is there an adjustment I can make to prevent this? I have the vacuum line connected to the connection point on the carb, not the intake. Nothing is binding it or stopping it from turning.

I left it off today by mistake and the idle dropped off. I turned it up and the engine sounded great I just didn't have any acceleration to speak of. When I reconnected it, the RPMs rose about 1K and didn't come back down. I could adjust the idle turn screw to bring it down but then it doesn't stay stable.

Maybe a vac line restrictor would help calm it down. Or maybe I just have it adjusted wrong.

Or maybe I just don't know what I'm doing (most likely).

[jetmechmarty]

T.C. (or anyone else)

My vacuum advance is not operating as I would expect.

Do you have a vacuum gauge tool, like maybe a Mity-Vac? There are instructions for testing the vacuum pot in the service manual.

[RichV]

Do you have a vacuum gauge tool, like maybe a Mity-Vac? There are instructions for testing the vacuum pot in the service manual.

Yes, I have one. I need to get a "T" connector to test it correctly. I had several but used them on other projects.

[MPittma100]

Rfi

All the caps I have come apart. I plan to leave the 5K ohm resistor in because of the interference issue. Hopefully the ones I ordered do come apart so I can swap the resistor. The were not that expensive.

The only interference caused by no resistor is to a radio (static).

The vacuum advance uses ported vacuum, not manifold vacuum. Therefore, there should be no vacuum to the advance at idle. Either the idle is too high or you have the advance hose installed onto the wrong fitting. The advance gets its vacuum from the fitting on the number 2 carburetor. It is the only carburetor with this fitting.

[TopCatGr58]

Hey Rich,

IIRC, you don't need a "T" fitting to TEST the vac. pot...just connect the mighty vack to the vac. hose and apply vac....doesn't the mighty vac have a built in vac. gauge in it...I don't have one?? IF it doesn't have a gauge...then yes I guess you WOULD need a "T" to have a gauge in line with the vac. pump.

Rich, the Vac. adv. doesn't really ADV that much with throttle input...it actually releases the adv. under strong load/throttle inputs....for the best power timing...it mostly engages under low throttle/cruising speed inputs to help provide more adv. time to burn the fuel mixture to provide better mileage, but once you crack the throttle open a bit, vac. drops and it actually retards timing back from the MAX 52 degrees fuel saving point down to the ~35 degrees max amount of optimum max power timing point!!

**edit...you said that it seemed like it didn't have any power when you capped off the vac. adv. pot...that shouldn't be so! The Cent. Adv. provides most of the adv. timing for POWER....and so IF you didn't have much power....thent that points to a possible problem with the cent. adv. parts...but I thought you said you had removed and cleaned/greased those parts????

As has been stated, you either have the main idle screw set too high so that the butteflies are opening too much which exposes the vac. port in the carb which then sends vac. to the timing adv. pot. You may need to adjust the pilot screws out a little more to keep it idling with the main idle screw backed off/down so that the butterflies can be more closed to prevent premature vac. signal to the vac. adv. pot.

I thought George helped you with the vac. synching of the carbs...which should have also done some pilot screw idle adjustments/tuning as well? Remember idle should be around 1000-1100 rpm....so if you're setting it much below that, that may also be why it can't maintain an idle.....but remember the bike isn't providing much/any charging current at that low an idle speed, and IF the battery is weak, it may be running too low of voltage for any time at that idle, and can also contribute to it not maintaining idle!?!? JAT!

The radio interference is only if you want to run a radio on your bike, listen to AM, or worried about causing the car next to you interference on their AM radio!?!? The TCI is not subject to the RF noise, and IF you are running the weak OEM spark plug coils...the higher resistance can actually cause a weaker spark....so as stated...if you are running resistor plugs you don't need the resistors in the caps! However, if you're using non-resistor plugs, it still doesn't hurt to NOT run resistor caps especially on the OLD OEM spark plug coils!

T.C.

[RichV]

The only interference caused by no resistor is to a radio (static).

The vacuum advance uses ported vacuum, not manifold vacuum. Therefore, there should be no vacuum to the advance at idle. Either the idle is too high or you have the advance hose installed onto the wrong fitting. The advance gets its vacuum from the fitting on the number 2 carburetor. It is the only carburetor with this fitting.

The idle was set to very low and the line is attached to the #2 carb (not manifold).

The bike has no trouble starting and it runs smoothly. I'm going to do a vacuum test once the heat dies down a bit to see what is going on with the pressure.

[RichV]

T.C.

George and I didn't get together due to family issues. I purchased a set of four vac gauges and used them to sync the carbs. My pilot screws are set to 1.25 turns and the bike idles at about 1K after I adjusted the main idle. Since I cleaned and swapped out the coils/caps I now idle without any problems. It will run forever.

My 1981 special does not have an inertial advance. Just he vac advance.

I put a vac gauge on the advance line to see what's going on. When idling at 1K (about). I get 20 mm of fluctuating vac on the line which is causing the advance to vibrate slightly causing a small variation in idle speed.

When I rev the engine, the advance turns CC as the vac increases on the line. When I release the throttle, the RPM drops and stops at 2K RPM and stays there. The advance stays slightly engaged and the vac on the line is elevated (didn't write it down - I'm a bad scientist)

I can manually turn the advance back and the idle will drop back to 1K RPM.

I did a quick bench test of the advance and was able to get movement with the slightest bit of vacuum. The vacuum advance diaphragm is fully engaged at about 90-100 mm which is lower than the 150mm in the manual.

As a side note: I don't have a good tach only the one provided on the bike which may not be accurate at low RPM. That said, I've been riding all my life and I know what an idle sounds like.

So my remaining problems are:
1. Sputtering during acceleration.
2. Plugs #2 and #3 carbon fowling.
3. Ignition advance does not return to idle position and reaches full advance at 90-100mm.
4. While idling, the #2 carb produces about 20mm on the vacuum line connect.

I currently have the following on order or on hand:
1. New plugs
2. New caps (on order)
3. New jets (on order). Main jet #115

So... Does it look like the vacuum advance diaphragm is bad? The spring inside is not strong enough to return the unit to idle?

[TopCatGr58]

Hey again,

Well, we know that the plugs will get fixed when you get the proper jets.

Well, the vac. adv. pot may be worn...or it may also be corroded on the piston actuator arm...and that's causing it to hang up and not release. You can take it off and inspect it, clean the arm etc. Double check where the arm attaches to the plate, folks have reported some spurs and such developing there which has caused the arm to get stuck/hang up and not fully release.

With the diaphragm it's usually that it get holes in it or leaks so that it doesn't pull enough. The 20mm hg vac at the carb at idle may be normal, I don't know for sure never having measured mine. But the port actuating at that lower vac. amount does sound suspect, and that you may be getting TOO MUCH Adv. at too low rpm which may also be contributing to your sputtering response...but you/we need to get the jets fixed first before tinkering too much with the adv. stuff.

Sorry about forgetting that it was the 81. Another test you can do is to just cap off the cap adv. port, the 81 TCI will provide the required timing adv. for all of the POWER the bike needs....you just won't have the fuel savings part/functionality. This way IF you still have the sputtering then you will have confirmed that the jets are junk and need replacing!

T.C.

[RichV]

During the period of time I left it off, the sputtering stopped and the power dropped off. I'll try capping it and seeing if the sputtering stops. It's obvious that something in the unit (which is sealed) provides the reverse force that the vacuum fights against has weakened. I have a second one but it's rusted and frozen. Maybe I'll cut it open to see what's inside.

That doesn't solve the mileage and fouled plug problem which now points to the #2 and #3 jets. By the end of the week, I should have the parts and fix the remaining problems.

I still have a bad seal (my fault) which is leaking oil. It's slow and I can still ride it. I just need to wear my rain gear.