Bringing My '79 Bonneville Special Back to Life

I was at a gathering in London many years ago, Les, when another American seriously asked a British lady if "y'all celebrate Thanksgiving."

"Yes," she replied, "but we celebrate it on the 4th of July." Since that is American Independence Day, the insinuation was, I think, that she was grateful to have gotten rid of the Americans. I thought it was a universal joke there.

Al

Tulsaalva said:

I was at a gathering in London many years ago, Les, when another American seriously asked a British lady if "y'all celebrate Thanksgiving."

"Yes," she replied, "but we celebrate it on the 4th of July." Since that is American Independence Day, the insinuation was, I think, that she was grateful to have gotten rid of the Americans. I thought it was a universal joke there.

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Al,

To be honest, I did have an idea of what you were hinting at! :wink:

Universal joke over here? No, not really .

A few weeks ago, the Bonneville started running poorly. It was getting cold so we put it into the storage room since I had the current Project 944 to work on.

A couple of days ago Seventeen extracted the bike and pulled the plugs. They were heavily sooted. We installed new ones and the bike started on the first kick.

It idles fine, but when Seventeen accelerated away down the street, the engine would start cutting out just over 2,000 RPM. There is a hint of black smoke when it does so.

Last Fall, the students at the Technical College removed the carbs, cleaned and reinstalled them. Is there an adjustment (perhaps the needles?) that might have been maladjusted?

The idle jet is adjusted out at one and one-quarter turns. It starts readily and idles fine at just over 1,000 RPM. My thought is that it should not need to idle so fast. True or false? Below that speed, the engine dies.

An angle-section bar, four to five inches long, was left out of the choke linkage when the carbs were reinstalled. It seems to be intended to connect the two carbs for the choke setting but we've not been able to figure out how.

The Triumph is now at home; the students are working on the Norton. Their previous instructor quit and moved to Texas. A new one has taken his place and seems to be much more capable. He is also showing a greater interest in the Commando.

Al

Tulsaalva said:

Last Fall, the students at the Technical College removed the carbs, cleaned and reinstalled them. Is there an adjustment (perhaps the needles?) that might have been maladjusted?

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The needle positions could be wrong? But without more detailed information about the setup I'm not sure I can offer any help, as the standard settings are included in the factory manual, and presumably, those have been checked against the carb settings already?
One major cause of richness in the Amal MkIIs are the choke plungers, if they are not seating fully, or if the rubber plunger tips have degraded then that could lead to rich running problems.
Also check the float heights.

Tulsaalva said:

The idle jet is adjusted out at one and one-quarter turns. It starts readily and idles fine at just over 1,000 RPM. My thought is that it should not need to idle so fast. True or false? Below that speed, the engine dies.

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Personally, I wouldn't want to set it much lower than about 1,000 RPM.

Thank you, Les! We appreciate your tips and will get right on it. We'll check the manual and look for any troubles in the carbs' installation.

The bike has been revving right up to 3000 rpm, then missing. When i go over 4000, though, it fires correctly again. However, this last time when I was riding, after about 8 miles, it started misfiring at every rpm, except idle. That leads me to believe the plugs have fouled again, and we have a rich fuel problem, I'm just not sure how to fix it.

Seventeen

Given where it seems to misbehave I'd also look at needle position first. Any chance you have the wrong jets or needles? I've seen that right from the factory and on old bikes it is quite common.

I think you're right, Cookie.

When we got these bikes into stock in 1979 in Germany, we found that the Specials would not run with Meriden's 2into1 exhaust system. We solved the problem by ordering Alphabet's 2into1 systems from California, an example of which is still on the bike. The original factory systems were thrown into a dumpster. Oh, how I wish I had them now! I'd be rich!

I'm sure the less restrictive Alphabet's system required different jets and needles. I was not the service manager, who is lost to me now, so I don't know what changes were made to make the bikes run properly. I do know that he was successful at that and at solving the oil pump problem.

I guess we'll have to experiment until it's right. Does anyone have a suggestion for a starting point? My guess is that we'll simply take the carbs apart, carefully reassemble them according to the manual, and go from there.

Al

That is always the starting point. Also check the size on each jet, if marked, against the manual. Some replacement stuff I've seen was not marked.
I also look for scratch marks that can indicate wear on jets and needles, I think you'll always see marks on the slides.
I bet there are a number of Triumph owners on the board who can help you more than I can. I don't have a Norton tatto but that is what I alsways bought for years. I only worked on Trs becuse my friends owned them.
I can't remember how we did it now, but we were able to put my spare Norton front end on my friend Rusty's 750 Triumph. This is bringing back memories.

Seventeen has been riding the Bonneville but it has started to run poorly. It will not idle. When he kicked it into life, holding the throttle open a bit, I thought I saw a puff of smoke come from where the head meets the cylinders. I wasn't sure.

Thinking it may have a blown head gasket, I did a compression check and found 100 psi in the left cylinder and 130 in the right. I'm sure that's not within specs but have not found anything in the manual which tells me what the specs should be.

My plan is to remove the head, have it trued (planed) and replace the head gasket.

Do y'all have any advice?

Al

There are a lot of bonnie folks here that will come to your aid, but if I saw a puff of smoke and had low compression that's where I'd start.

150 - 180 on both jugs is average, depending on ring condition.

I like solid copper head gaskets on Bonnies.

I'm sure you are going to check the valves while you have the head off.

Tulsaalva said:

Thinking it may have a blown head gasket, I did a compression check and found 100 psi in the left cylinder and 130 in the right. I'm sure that's not within specs but have not found anything in the manual which tells me what the specs should be.

My plan is to remove the head, have it trued (planed) and replace the head gasket.

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Head gaskets do blow occasionally, and it could be "just one of those things" that can happen, and could be cured simply by fitting a new (composite) head gasket?

I would certainly check that the head is actually in need of truing before doing so. As with all British bikes, it's a good idea to re-torque the head periodically to help prevent it happening.

I'd be most concerned with the difference but did you take the test with throttle and choke open and kick until it stops going up?

grandpaul said:

150 - 180 on both jugs is average, depending on ring condition.

I like solid copper head gaskets on Bonnies.

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Thanks, Grandpaul! That's exactly the information I've been looking for. Is it in the workshop manual?

Al

Cookie said:

I'm sure you are going to check the valves while you have the head off.

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Absolutely, Cookie. LaNelle recommended a machine shop that has done British bikes for her for years. I plan to take the head to them and have them check it out completely.

Al

L.A.B. said:

Tulsaalva said:

Thinking it may have a blown head gasket, I did a compression check and found 100 psi in the left cylinder and 130 in the right. I'm sure that's not within specs but have not found anything in the manual which tells me what the specs should be.

My plan is to remove the head, have it trued (planed) and replace the head gasket.

Click to expand...

Head gaskets do blow occasionally, and it could be "just one of those things" that can happen, and could be cured simply by fitting a new (composite) head gasket?

I would certainly check that the head is actually in need of truing before doing so. As with all British bikes, it's a good idea to re-torque the head periodically to help prevent it happening.

Click to expand...

I have a follow up question on this, Les, based on what I read in the Service Manual. I need to read it again and will return later to ask it.

Thanks!
Al

Cookie said:

I'd be most concerned with the difference but did you take the test with throttle and choke open and kick until it stops going up?

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We did kick the bike until the gauge quit moving, Cookie, but I'm not really sure if Seventeen (who was on the bike kicking it) held the throttle open. I'm sure I didn't remember to tell him to do so. Just to make sure, we'll re-do the compression test and report back. I knew that and should have remembered it. Thank you!

Al

Generally if you are low on one side you want to find out why, seems like the training book told us more than 10% variation was time to disassemble and inspect, but that was years ago. All you will gain from the test will be to see if you meet the spcs GP posted. Put a bit of oil in and check it again, if it comes up you might need rings.

Damn! Seventeen and I redid the compression check on the Bonneville. The first retest with the throttle fully open yielded the same results, 110 in the left and 130 in the right. After adding a squirt of oil to both cylinders we got over 160 on both. I guess we have a ring problem and the engine will have to come out for a rebuild!

My worry, though, is that we have an oiling problem leading to ring failure in less than 2,000 miles. There was a problem with the oil pump on earlier '79s, both D and E models. A two chamber oil pump was used. That pump had two ball bearings that were held in place by springs, intended to stop the oil from flowing backwards. Our service manager traced the failures to an elliptical seat, causing the spherical ball to not seal. Peter Britton, the export sales manager at Meriden at the time, then traced the problem to a worker who was not properly seating the ball. The system used was to drop the ball into position and, using a punch, rap the ball smartly so that it formed the seat in the softer brass pump body. She was bored from years of the same work, and wasn't doing the job correctly. The punch had to be held perfectly straight; she was hitting it at an angle.

Our service manager solved the problem by asking a local German machinist to make a punch-like tool out of hardened steel which was essentially a ball bearing with a guide that fit down into the pump and held the ball straight. When the other end was rapped, the seat had to be formed perfectly round. Just to be sure, the ball was dropped into place and rapped again. We had several of the tools made and sent some to Meriden along with instructions for their use.

Meriden, in the meantime, had developed a three chambered pump which was intended to produce higher oil pressure. An attempt was made to retro-fit all the bikes we sold with the new pump but I don't know if our Bonny got the upgrade or not. I soon will.

Thanks, Y'all! I'll update this as soon as I have more information.

Al