79-81 motor swap starting problems

[kenkrieger]

I have swapped a 79 special motor into my 81 frame while i rebuild my 81 motor.
I went thru all electrical schematics prior to doing this swap and all connectors are the same on both motors.
- I have retained all the 81 electronics and wiring
- I removed the 79 ignition advance and put my 81 advance on the 79 motor
- 79 motor needed oil seals so I replaced them, motor ran fine prior to the oil seal job
- Cams are all back in there correct spots, all dots line up, all arrows correct and dry runs through have the cams and lines at the rightspot, and valves in the correct sequence for number 1
- Coils are 81 - and read 27K on both, coils without the caps are 12K, caps read 7K, engine ran fine before I lost a bearing
- Coils ins are 1.5 ohms - rotation with number 1 out shows a blue spark, each time the pickup coils are run past.
- cylinder shows gas when i try starting up with everything in place
- problem is no proper ignition, and a backfire with smoke thru the car, followed by a samll back fire from the exhaust.
- I have gone throught the cam setup half a dozen times, they are properly aligned
- so I needed to bounce this off you folks to see what I am missing here,,
- been working on this bike for 9 years now, and have never not got it running when i had problems,,, more than 60K miles so not gonna give up now.
Thx for any ideas or advice.

KJK

[bikerphil]

When replacing the ignition assembly under left side cover, it is possible to inadvertently put the reluctor on 180 degrees off. With the cam dot lined up, it should be pointing at the top P/U coil. HTH

[Guy_b_g]

Shouldn't the coils on an 81 be 3 ohms?

**editted, not 3K ohms for primary resistance! ** TC

[DGXSER]

I've not had the pick up coils off, but I have been involved in exactly the same swap before (ok actually 79-80 in an 81 bike).

Had a very similar problem when sarting up and found the pickup coils were swapped. Swapped the wires feeding the coils (grey and orange wires). That corrected the issue.

[kenkrieger]

Yep the reluctor is pointing at the top pickup coil. It has a tab on the motor and acorresponding groove on the reluctor that only allows one way installation.
- the coils are supposed to be 1.5 ohms by the Manual I have,,let me double check
- I never had the coiwires out of the connectors so no swap occurred, if I understand you correctly.
Many thx for all the replies, gonna check on the input resistance

KJK

[DGXSER]

As stated,I have nto done any of this work. However, I was there when another member installed the pick up coils and the timing assembly off of one bike on another. As it turned out, he got the pick up coils mounted backwards, so the pick up coil was sending the signal to the TCI to fire 1 and 4 when it should have been signaling 2 and 3. We switched the connectors form the TCI to the coils and the bike fired up.

[kenkrieger]

Now I understand, that is entirely possible,,,gonna see if thats the problem,,,I thought this might be a problem but couldn't find anything in my Clymer junk manual,,,many thx.

KJK

[TopCatGr58]

Hey there Ken,

Nice to see you on here, sorry to see that it's under these circumstances!

Guy's right though, that the 81's primary resistances should be about 2.5 ohms, not 1.5. The secondary's are within spec for the 81, they ARE different than the 78-80 which were 15k.

Hope it was/is just he pu coil assembly on backwards, sounds like the most probable scenario from what you've said!
T.C.

[skids]

If the pickup coils are reversed, couldn't you check this by switching plug wires from the 1-4 cyls with the 2-3 cyls? (assuming the wires will reach)

[Incubus]

It would be much easier to switch the orange and grey wires at the coils. I know they reach.

Patrick

[kenkrieger]

I did the fix for the pickup coils as soon as I bought the bike,,,and cut the wires specifically to the right length for the top and bottom, and marked them.
So when mounting them I put them back where they were supposed to go,which is why I didn't go there first.
- this leads me to believe the 79 is 180 degrees out from the 81,,
- I got the motor to run this morning albiet a bit ruff with starting fluid,,it hasn't run for years. So either way it was the problem. So far not running on its own, seems to be starved for gas, and have an exhaust leak, so back to the carbs and exhaust for now.
- many thx for the assistance as always you can get another look here, and usually the solution.
- no worries about the bike Top Cat,,I have the 06 VMAX to hop on for a ride,,,actually sounds like a good idea.