'72 Norton bogs down after less than 10 miles - need ideas!

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PJ Martel

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First time posting, and I need some suggestions. After forty plus years of riding, restoring, and selling a ridiculous number of Triumphs, I finally decided to take the plunge and purchase a Norton. She's a 1972 Interstate, single mikuni VM34, single 12 volt coil with a boyer ignition. The first couple of hundred miles she ran pretty smoothly, then she started developing an annoying habit of suddenly "bogging down". The began to happen after 30 miles or so, but nnow I just took her out and it started after just 6 miles. I'll give it some throttle, and it won't respond unless I get the rpm's up there, and then it's like hitting a switch and it will run fine fine until I lower the rpm's and then I can't increase the speed again unless I pull in the clutch and rev it up. When it's acting this way, if I try to let her idle she'll die. On one run on the highway no matter what I did, I couldn't get the revs up and top speed was about 50-55. She's a little cold blooded to start (and enjoys kicking back a me), but once warm settles into a nice idle, and the first few miles are fine. I took a look in the tank and discovered a paper towel left by the PO who had just completed a total restoration. I thought that was the problem, so I cleaned the tank, put on new peacocks and fuel line, dismantled and cleaned the carb, new plugs (which are the correct color), and it hasn't made any difference. The bike is absolutely stunning, but I would really like to be able to take her out more than a few blocks. Maybe this is the Triumph gods punishing me for breaking my decades old allegiance. Any suggestions would be greatly appreciated.

Thanks,
PJ Martel
 
Re: '72 Norton bogs down after less than 10 miles - need ide

not that it may be your entire problem (or having anything to do with it) but kicking back at start up suggest the timing is to advanced or the battery is low (if you have an EI like a boyer) - does the bike have the points still or an EI and hows the battery? seeing as you have to raise the RPMs to get the bike to run properly (and an EI with a low charge can misfire) perhaps the higher RPMs give enough juice to fire and when the RPMS drop the EI misfires -just a thought



PJ Martel said:
First time posting, and I need some suggestions. After forty plus years of riding, restoring, and selling a ridiculous number of Triumphs, I finally decided to take the plunge and purchase a Norton. She's a 1972 Interstate, single mikuni VM34, single 12 volt coil with a boyer ignition. The first couple of hundred miles she ran pretty smoothly, then she started developing an annoying habit of suddenly "bogging down". The began to happen after 30 miles or so, but nnow I just took her out and it started after just 6 miles. I'll give it some throttle, and it won't respond unless I get the rpm's up there, and then it's like hitting a switch and it will run fine fine until I lower the rpm's and then I can't increase the speed again unless I pull in the clutch and rev it up. When it's acting this way, if I try to let her idle she'll die. On one run on the highway no matter what I did, I couldn't get the revs up and top speed was about 50-55. She's a little cold blooded to start (and enjoys kicking back a me), but once warm settles into a nice idle, and the first few miles are fine. I took a look in the tank and discovered a paper towel left by the PO who had just completed a total restoration. I thought that was the problem, so I cleaned the tank, put on new peacocks and fuel line, dismantled and cleaned the carb, new plugs (which are the correct color), and it hasn't made any difference. The bike is absolutely stunning, but I would really like to be able to take her out more than a few blocks. Maybe this is the Triumph gods punishing me for breaking my decades old allegiance. Any suggestions would be greatly appreciated.

Thanks,
PJ Martel
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Re: '72 Norton bogs down after less than 10 miles - need ide

yep


first do the easy stuff

how old is the battery, do you keep it fully charged - if older Boyer analog EI batt must be kept charged

is it possible your battery is charging from your charger but not charging while riding the bike?

I would take out your volt meter and hook it up to the battery, start bike and see what volts it reads at idle
and then rev it up to say 3000rpm and see if the volts go up, if so it shows alternator is sending AC back and yes it is being converted to DC and charging batt while riding

if that simple test checks out ok then I would put a strobe light on the primary mark and blip the revs
up to almost 5K (analog boyer) and see if it reads around 30 degrees (think boyer is 31 at 5K),
the kick back starting is either too tentative of a kicking prod or too advanced in the timing

lastly, it is possible you have a partially blocked main jet in the Mikuni or maybe the needle is stuck partially
sideways in its clip, very easy to take the top off the mikuni off and lift out the slide and cable together to see if the needle and clip are secure, take the bottom of the mikuni off and the main jet is right there to unscrew and see if the hole is clear
 
Re: '72 Norton bogs down after less than 10 miles - need ide

Blocked vent hole in fuel tank cap? Crap in filter screens inside fuel tank?
 
Re: '72 Norton bogs down after less than 10 miles - need ide

Look for the production date on the battery . On a high vibration machine such as our beloved Nortons they tend to croak after 4 or 5 years usage. I use Gel type glass Mat type to extend life. Go there first then explore paper towel residue bits blockages. :|
 
Re: '72 Norton bogs down after less than 10 miles - need ide

After discovering the uninvited guest in the tank, the entire fuel system was clean out completely. As far as the tank vent, when it has acted up, I've opened the cap to see if would make any difference, and it didn't.

PJ
 
Re: '72 Norton bogs down after less than 10 miles - need ide

Just checked voltage -12.73 before start, the same to 12.88 at idle, increases to 13.12+ at 4000 rpm. The idle is fine, but I do need to check the timing before she beats the crap out of me! I'll have to get to it Saturday, as I work tomorrow (24 hr shifts). In the meantime, anything you can think of would be appreciated. I'll see if I can post some pics of her.

PJ Martel
 
Re: '72 Norton bogs down after less than 10 miles - need ide

Carb is funky. A proper bath in Berryman's Chem-Dip will likely improve things. Save this possibility for the point where you've exhausted the several free things to check. Chem-Dip is like $16+

Welcome to the forum, PJ
 
Re: '72 Norton bogs down after less than 10 miles - need ide

Thanks GrandPaul, I'll give it a try as I'm never without a gallon of Berrymans. I initially cleaned them just with a spray cleaner as it looked pretty pristine when I took it apart (no junk or varnish). I just find it odd that it would start up, idle smoothly, and run well for a few miles before starting to act up. I also always use ethanol free gas in all my bikes. Good to see you on this forum - your advice has helped me many a time with my Triumph throughout the years.

PJ Martel
 
Re: '72 Norton bogs down after less than 10 miles - need ide

Strange as any Commando mystery I've heard. I've had chokes engage to similar but with misfires roughness loss of power but noticed early on taking off on road w/o much delay of onset. Low voltage on most electro brain ignitions at road speed will also loose power but with rough tuning to horrific back firing stalls, either way can't ride on as its gets so bad pretty fast. I've had water do this but with towel and cleaned out fuel system you covered that. Does sound like its running out of fuel flow though. Maybe one tap open ain't enough in your case but usually only shows up trying to keep up with sports bikes on freeways. Such a simple machine what could go wrong all the Truimph guys told me too.
 
Re: '72 Norton bogs down after less than 10 miles - need ide

Hobot - strange indeed. As I stated in my initial post, I'm no stranger to Brit bikes (Triumphs), but I've never run across a problem with these symptoms. I'll keep trying things and your guys suggestions and sooner or later (hopefully sooner) she'll be running right. I've never run across a problem that I couldn't eventually solve (many times with assistance from others), and I will not be defeated! I have found out that it is indeed not nice to piss off the Triumph gods!!!

PJ
 
Re: '72 Norton bogs down after less than 10 miles - need ide

Coil failing after heating up? Had similar experience on my Goldwing. Coil pack on one side was failing and taking out two cylinders.
 
Re: '72 Norton bogs down after less than 10 miles - need ide

One additional bit of info on this problem - when she starts having the issues I've described, I'll stop and shut her down for about 10 minutes. She'll start right up, and run just fine for 6-10 miles before the issues return.

PJ
 
Re: '72 Norton bogs down after less than 10 miles - need ide

Drones76 - that is an item on my list to check as I too have had one crap out when it got toasty. I'm sure I've got a 12v coil stored somewhere that I'll try swapping out. If not I'll wait until Monday and replace it with the one that comes with the Power Arc.

PJ
 
Re: '72 Norton bogs down after less than 10 miles - need ide

PJ, I'm tickled no end with your frustration as relieves my sense of wits not having a cycle back ground but with Combats which still educate me routinely. The coils I've had fail either stopped one side firing "after" some heat+vibes shorting it or just wouldn't fire on that coil at all. None of them failed in such a way as to smoothly decease power-speed as main symptom. Look at it after dark for something reasonable to do in mean time. Don't think rear brake drag could slow down a Commando that much but an example of how to think with Commando symptoms. My lawmower got slower and slower last year till wouldn't run, turned out to be oval worn bores losing compression.
 
Re: '72 Norton bogs down after less than 10 miles - need ide

Not coils. Not compression /?. Need more info. Ignition system ??? Credit card health ? Get to work,battery health then check fuel flow. 24 hrs. work is illegal. I work 12 hrs. tomorrow, max. by law.
 
Re: '72 Norton bogs down after less than 10 miles - need ide

A couple of years ago my Commando suffered from poor running, tried everything.
It turned out to be internal breakage if the ignition wiring, causing intermittent electrical contact.
This was in the area where the wiring enters the contact breaker cavity.
 
Re: '72 Norton bogs down after less than 10 miles - need ide

Could be the carb's float level is too low, running out of fuel.
Jaydee
 
Re: '72 Norton bogs down after less than 10 miles - need ide

The description like hitting a switch with the revs up indicates the carbs are flowing ok thru main and needle jets. With blocked idle jets it wont run under 2000/2500 no load. Does it still idle OK after it acts up but wont run unless the revs are coaxed up. If so then its not the idle jets. Does putting the choke on improve things when it starts bogging? Are the chokes (do you have any?) fully open after starting (stupid question I know but maybe yr Triumph didn't have them?)
 
Re: '72 Norton bogs down after less than 10 miles - need ide

For extra credit check all air seals, x-over tube to exhaust roses. Replace fancy key fob with a feather or yarn.
 
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