Running 1975 cams and carbs on a 1979 engine block

[1983lux]

Hi all, I bought a Randakk kit for my 1975 GL1000 last year and rebuilt my carbs over the winter. I have just recently installed the rebuilt carbs on my bike, but they are not idling very well. This could be for a number of reasons, so I'll get into the bike's history.

The bike is a stock 1975 model, I drove it around for a while but it ended up blowing a conrod bearing (I think it was because I stupidly drove it around with too much Seafoam in the oil too long, trying to fix the sticking starter clutch without pulling the engine). So, I bought a cheap, running 1979 parts bike with 1982 GL1100 carbs on it and I believe a 'Dyna S' ignition system. I installed the 1979 engine w/ 1982 carbs on my 1975 bike and drove it around for another couple of years. The 1982 carbs started leaking, so I thought I might as well rebuild my original 1975 carbs, re-install the original 1975 cams on the bike, and go with the reportedly higher-performance early GL1000 setup.

I recently installed the 1975 cams and rockers in the 1979 heads. After putting the '75 cam in, I reinstalled the Dyna S ignition module that came with the 1979 without changing anything. I started the bike up (still with the leaky 1982 carbs on) to see how it ran, I didn't let it warm up (it was in the garage and I didn't want to smoke it up too much), but it seemed to run quite well at a couple thousand RPM before I shut it down. I then installed my freshly rebuilt 1975 carbs on the engine.

I started up the bike today, and it did so relatively easily. However, the bike seems slow to decelerate. When I give it a shot of gas, it'll hover at about 2000rpm for quite a while before dropping down slowly into a near-stall chugging idle. If I turn the idle screw, the bike will run better, but after giving it another shot of gas it'll continue to rev too high (2000+) RPM for about 20 seconds before eventually slowing down. Not much fun driving around revving like crazy at stoplights, or feathering the throttle all the time.

So, my question is, are there any timing issues I've created by running 1975 cams on a 1979 engine block with a Dyna-S which was set up for 1979? Can I still trust my 'T1' and 'F1' marks when using a 1979 block with 1975 cams? I don't want to start chasing carb gremlins if my timing has been thrown off. That being said, if my symptoms sound like they are due to a common carb re-assembly mistake, that'd be good to know.

Maybe I could take some pictures of the timing unit to help figure things out.

Thanks for any help!

-Jesse

[Whiskerfish]

Yea you have a mix match system. Which advancer did you use? The timing index mark on the crank is different so if using that to set your timing it will not be optimum. The 79 crank is marked at 10 degrees and for a 75 setup you want 5 degrees and the early style advancer. When the engines were re-tuned in 78 the advancer curve also changed.

Be prepared you will see a fairly significant drop in fuel economy with this setup compared to how you had it previously.

I would reset the timing and if your issues still exist then look to the carbs. First things to check with a hanging idle is vacuum leaks and proper throttle cable routing/operation/free play.

[1983lux]

Ahhh, that's it. I stumbled upon this right before getting your reply: http://www.randakksblog.com/performance ... 0-engines/

I did not swap out the advancer since they looked the same to me. I will swap in the 1975 advancer, I strongly suspect that could fix it. I really didn't want to take those carbs back off, haha. Hmm, I didn't know that my previous setup would've been more efficient. I struggled when deciding whether to rebuild the Gl1100 carbs and leave the cams alone or go with the 1975 setup. Lots of differing opinions on the topic. This will be the first time running the bike with properly working carbs so I'm really looking forward to a good run.

If further timing is required, I'll make sure to make the new marks on my crank. I'll report back when swap is complete.

[Whiskerfish]

For your hanging idle make sure to get it up to full temp then crank down on those intake boot clamps just about as hard as you can. Doing it cold is almost useless. you want that rubber to be good and warm so it will flex.

[robin1731]

Have you synced the carbs? Checked for vacuum leaks? Need to do those too.

.

[1983lux]

UPDATE:

So I had some time to mess around with the bike today and try out some of these suggestions. Thanks for all the help I've received so far! Still having some issues though.

1. I swapped in the 1975 mechanical advancer. Definitely improved the smoothness of the bike a little, and it feels more powerful when driving down the road, but didn't fix the hanging idle issue. I have not yet re-set the timing (need to read up and remember how to do it, will also read Randakk's split timing tips).

2. After a few runs around the block to heat up the bike to running temp, I tightened up the intake boot clamps. There was room to tighten them for sure. Almost seems like the clamps reached the end of their range while I could still turn the screw without a whole lot of effort. Maybe they are worn out a bit? Would a regular hose clamp be an ugly, but better functioning replacement? Maybe I should look at the clamps on the old set of carbs...

3. Thinking back, I did set my valve lash just after installing the 1975 cams (might as well do it while the covers are off, right?). However, I used the original 1979 T-1 mark to do it. Was this a mistake, or is it only the timing adjustments that need the 5 degrees BTDC mark?

4. I have noticed a weird symptom. My choke basically doesn't do anything through most of its travel, and when its full out it will make the bike stumble and shut off. I would expect my idle to increase sharply as I pull out the choke like it used to. The cable appears to be hooked up right and the linkage moves normally (though the cable is stiff and needs replacement). Does this indicate a vacuum leak letting air get around the choke perhaps, or maybe I made a mistake hooking up the choke linkage somehow?

5. Checked throttle cable. Also should be replaced soon as it doesn't spring back to idle well on its own, but the linkage appears to be moving through its normal range properly. The same cable also worked fine with the old carbs so I doubt that's it.

6. robin1731 - I have not yet synced the carbs, I don't have the vacuum gauges to do it. I was thinking that maybe I'd take it to the local shop to have it done, but I wanted to rule out all other possibilities first before handing it over. Those guys are pretty expensive, and I probably can't afford to have them chase down other issues if the sync isn't working out. Might be able to look up the PO, he said he had a set of gauges and might be willing to help out if I ever needed em (that was several years ago though, haha)

I have also not checked for vacuum leaks. How would I go about doing this? Any way to pin down where the leak might be coming from?

Lastly, I took a quick video of the bike running. I tried to pull my choke out to demonstrate that it doesn't really do anything, but the old cable is too stiff for me to pull without using my other hand to push on the linkage, haha. You'll notice that the bike idles around 2000 RPM. As soon as I put the bike in 1st gear and let out the clutch a little, the idle will slow down to about 1000rpm and stay there even after I go back into neutral. If I give the bike another shot of gas, it will return to idling at 2000rpm and stay there. I also notice a weird squealy noise coming from the left side of the engine that wasn't there before (you can hear it in the video a bit). Any thoughts welcome! Hopefully the sound helps with diagnosis.

https://www.youtube.com/watch?v=YrM9uHDFNNU

In the meantime, I will try timing the bike on my own, and maybe re-setting the valve lash using the 5 degs BTDC mark if that is what I was supposed to do.

[Whiskerfish]

The throttle has to SNAP back or you will never get the carbs right.

[wingrider]

Randakk has some new fangled clamps that do a lot better at clamping then the originals.

[robin1731]

The valve adjustment should be fine where you set it. The T mark on the crank is no different from year to year.

Yes when you pull the choke lever the idle should increase. If all the mechanical linkage is hooked up and operating correctly. But not if the idle is already so high that it doesn't reach that point.

Without syncing you will be chasing your tail on some of this.

Like WF said they should snap back pretty good. Does the linkage snap back without the throttle cables hooked up?

.

[1983lux]

Hey guys,

Sorry to revive my old thread but thought I'd post my solution in case anyone else comes across similar problems with a hanging idle. I had three issues:

1. Must've forgot that the two new o-rings I put on the bottom of the air-cutoff valve were barely on there, and they fell off during the carb install onto the bike without me noticing. Used a touch of seal-all to hold them in place then re-attached it with the o-rings where they should be. Didn't fix the problem but made it a bit better.

2. Only the 'pull' cable was hooked up to the throttle. Hooked up the 'push' cable as well and that helped make sure the throttle was fully closing as it should. Lubed up both cables. Nonetheless, the cables are not perfectly smooth and I will replace them soon.

3. Remembered the PO saying something about having a set of vacuum gauges when I bought the bike years ago, found his number and he was happy to sync it up for me. That seemed to fix my hanging idle right up. The gauges were all over the place before the sync.

All I can say is, wow! I should've rebuilt my carbs a long time ago. The bike ran okay with the old leaky ones, but it absolutely hauls now!

[Sidecar Bob]

The carbs should be synched any time you have worked on them. And (as someone told you last month) the "hanging" idle is the classic symptom that they aren't in synch.