Carb Diaphragm Failure Troubleshooting

[LarryC]

I started a discussion in another post because I have been experiencing a somewhat sudden loss of fuel efficiency (49 to 35mpg). (My apologies if this is considered a cross-post). Bike appears to run fine but after exhausting all my other ideas on the cause (dirty air filter, synchronization, valve adjustments etc.) I'm thinking I may have some diaphragm failure and am wondering if others may have had similar experience with some loss of mpg before a noticeable drop in performance. That would certainly help with my diagnostics before tearing into the carbs. My thinking is, I may have only one or two diaphragms on the way out and that things will gradually worsen until I begin to feel the performance drop-off.

 

[Dinkie Diesel]

You might want to send George a private message. I believe I remember him having a similar situation. And he would know. Also try John Oosterhuis. They know the 1100 inside and out.

 

[George]

I didn't notice so much loss of MPG, but very significant loss of performance. Had to down shift on the uphill, and top speed dropped to about 80 MPH at full throttle. Found all 4 diaphragms torn and still attribute it to Iowa gas.

I had (have) a spare set of carbs so replacement of diaphragms was easy. Got another set of spares from Don Cortez (much cheaper than buying new) so I'm still ready for failure if it should occur.

There is some info on the 'net about "repairing" torn diaphragms but mine were all totalled. No chance of fixing them.

Another option, just buy a new bike. I did, after TWO major problems with ReSTored (afore mentiond diaphragms plus the cracked water jacket on the upper block.) "She" is now semi-retired and awaiting a complete sex change, uh, er, engine replacement. He'll re-emerge this fall as STanley, as in STanley STeamer.

<edit> Meant to add, dragging brakes can cause sudden loss of gas mileage, and other problems as well. Check the brakes closely and take appropriate action.

 

[LarryC]

You might want to send George a private message. I believe I remember him having a similar situation. And he would know. Also try John Oosterhuis. They know the 1100 inside and out.

Thanks Dinkie, I wrote to George and I suppose it wouldn't hurt to copy John on it too.
Larry

 

[George]

Thanks Dinkie, I wrote to George and I suppose it wouldn't hurt to copy John on it too.
Larry

Lots of info at st-riders.net too (beating John Oo to the punch. ) Also, Rob Parker, who has already chimed in here, is one of the best ST mechanics around. Heed his advice.

 

[LarryC]

I didn't notice so much loss of MPG, but very significant loss of performance. Had to down shift on the uphill, and top speed dropped to about 80 MPH at full throttle. Found all 4 diaphragms torn and still attribute it to Iowa gas.

That's my problem, I'm not noticing any performance drops..

I had (have) a spare set of carbs so replacement of diaphragms was easy. Got another set of spares from Don Cortez (much cheaper than buying new) so I'm still ready for failure if it should occur.

Have my eye on a set on eBay and made an offer, wouldn't hurt to have a spare set...

There is some info on the 'net about "repairing" torn diaphragms but mine were all totalled. No chance of fixing them.

I'm usually a MR Fixit so will look ito that too.

Another option, just buy a new bike.

Been unemployed over a year so that's not an option unless I find a deranged woman willing to finance me. Since I'm divorced 4 years already I don't see that happening anytime soon.

Meant to add, dragging brakes can cause sudden loss of gas mileage, and other problems as well. Check the brakes closely and take appropriate action.

Just did the front brakes a couple days ago and they were wearing evenly as far as I can tell. The pistons weren't as easy to compress as I'd like but I know I rebuilt the calipers two years ago with new rubber rings, seals and a good cleaning. They didn't appear to be dragging and don't run hot. Waiting for a new set for the rear to be delivered any day because I know they're getting down there too...

Thanks George

 

[LarryC]

My 93 had 4 torn diaphragms last year @ 178k miles. Symptoms were a gradual reduction of power and loss of fuel economy. It's very easy to just pop out the carburetors and inspect the diaphragms. The difficulty lies in paying for new ones. Ouch!

Thanks Rob,
I'm just trying to gather info on the slider failures. Is there rhyme or reason as to when or why they fail? I only have 78k miles on em.

 

[BuddingGeezer]

I have repaired a torn Cv carb diaphragm using 'Seal All'. The tear was a small tear on the outside edge of the diaphragm. like Brylcream, "just a little dab 'ill do ya". Carb worked great.

I have heard of repairing diaphragms with a 3M rubber spray. I probably wouldn't try to repair multiple holes or any hole that wasn't on the outside edge.

If there is no loss of last 1/3 or the throttle performance, the're probably not torn.

Ralph Sims

 

[LarryC]

You might also consider a compression test.

Bouncing back to this post. I think I've found the problem with the ign coils showing too high a resistance on the primary side. Found a used set on eBay and will post again if that solves the poor mileage problem.

 

[STPaulK]

Generally coils short when they fail (low resistance) or open (extremely high, or no resistance). What readings did you get?

 

[Doodaa]

Bouncing back to this post. I think I've found the problem with the ign coils showing too high a resistance on the primary side. Found a used set on eBay and will post again if that solves the poor mileage problem.

Been following your other post, if your plugs look good, I think I'd look elsewhere and save your money for the real problem. If your plugs fire good, your coils must be workin ok

 

[LarryC]

Been following your other post, if your plugs look good, I think I'd look elsewhere and save your money for the real problem. If your plugs fire good, your coils must be workin ok

According to the manual, the primary resistance is higher than spec. My buddy says the exhaust smells rich. I just don't know where else to look for a solution. What else can make my mileage drop so hard? I've even changed the carbs (I don't mind having a spare set). I've checked the valves, synchronized the carbs, checked for leaks. 48mpg to 32 is a major drop. I'm not a parts changer but I'm really tired of pulling tupperware especially in the middle of a heatwave.

 

[LarryC]

Have you tested the plug wires and caps? These have been known to fail upon rare occasion.

You know, I wasn't able to get a reading on the secondary side and perhaps have bad wires. That was the reason I ordered another set of coils and wires. I don't want to tear into all that plastic to get in there and not have a replacement on hand. If I find a bad wire I suppose I can just replace it but if the coils are bad it's much cheaper eBaying than running to the dealer. I don't mind have a few spares laying around if I'm wrong. Working in this stinking hot weather doesn't help my mood much either...

 

[LarryC]

Hey good news for you! The heat wave appears to be over.

Hawkeye, lQQking at your photo gives me the chills! lol Just missed last years Sturgis hail show but caught sleet in Idaho and snow near Vail.

 

[LarryC]

LOL that photo was taken in the summer time... about 13,000' up Mt. Evans. Also caught snow in the Black Hills and 123 degrees in Death Valley on that same trip. Fun.

Been up top of Mt Evans a few times. Once when it was almost 90 in Denver it was 38 and blowing hard. We stayed about 5 min before heading back down. Was up that way last summer and rode the OMG road where you could see Mt Evans. My buddy's lived in Denver and been riding those mts for about 30 years. He knows some great roads. Thought about riding across Death Valley last summer too, I came to my senses! lol

 

[LarryC]

Generally coils short when they fail (low resistance) or open (extremely high, or no resistance). What readings did you get?

According to the manual I should be seeing 2.16 - 3.9 on the primary side and I'm getting about 4.6 (now with 2 pairs of coils). I have no idea how true my digital VOM is (Fluke 11) but with very consistent reading over 4 different coils I'll venture a guess it's off and the coils are all good. Since I'm getting spark at both coils (looked kind of weak) I'm guessing the pulse generator is working fine so I'm thinking it may be the ICM. Manual says I should see battery voltage but I'm actually seeing almost a 1 volt drop. Suggestions? I'm going back out to try and see where the loss is but 1 volt prob. normal... Anyone hear of a bad ICM causing poor mileage or insufficient spark?