Short, irregular bursts of power and lagging.

[SolidGhost]

I just got this bike (77xs) and had it gone over. New exhaust (headers and mufflers). Mechanic road tested it, I rode it home from the shop (20min or so highway) then I rode it to work and back 40-60 min depending on whether highway or back roads) two days. I did leave the choke on and fouled the plugs (champion n7yc). Replaced them with NGK bpr7eix (iridium). A little on the way to work and for far too much of the return trip I felt irregular bursts like my bike was being pulled forward then losing power. I’d hoped it was just misfiring because of the plugs but no. Replaced them with the non-iridium equivalent and the problem persists.

I’m new to anything other than 60s Triumph and while I suspect this problem could be pretty universal, and dare I say obvious, I wondered if you guys had a first place to look. Thanks, all.

 

[Jan_P]

If same on both sides
I would start check the fuse holder
Then measure Voltage across battery. Off and On Revving se what it charges
Is it a stock Points bike ?

 

[JJames]

The fuse block and low battery voltage would both be likely culprits. The use block often overlooked as it may look alright. Give everything a gentle tug. Switch tank to reserve?

 

[SolidGhost]

If same on both sides
I would start check the fuse holder
Then measure Voltage across battery. Off and On Revving se what it charges
Is it a stock Points bike ?

New fuse holder as the old glass tube holder was upgraded to blade type when it was discovered to be the source of a short. New AGM battery but will test too. It is stock points. Thanks for giving me a place to start.

 

[SolidGhost]

The fuse block and low battery voltage would both be likely culprits. The use block often overlooked as it may look alright. Give everything a gentle tug. Switch tank to reserve?

Thanks, I will look there as well. I’m not sure my peacocks are set up right. I ran out of gas (fortunately a block from home) switched it to reserve, and there was nothing there.

 

[Jim]

Thanks, I will look there as well. I’m not sure my peacocks are set up right. I ran out of gas (fortunately a block from home) switched it to reserve, and there was nothing there.

I hate when my peacocks do that.

 

[GLJ]

It sounds like your problem may be a fuel issue. Might not be the carbs. Start at the beginning. Fuel delivery to them. Unhook the the petcocks and run lines to a gallon container. See if it will fill it with a steady flow. There's filters in the petcocks and on the stand pipes. Also a vent filter in the gas cap.

 

[Jan_P]

I would focus on the charging Check First .. It is simple to do .. Se what the charging voltage is when machine warm

 

[JJames]

I hate when my peacocks do that.

My (pet) peacocks!
Got et by my fork Gators!

Sorry. Too much coffee!

 

[XSTime]

Looking at your XS pics you do seem lucky enough to have those early version 78 vacuum peacocks.
Those early ones are the best and most trustworthy!
If you order a rebuild kit be careful. The next mass produced version as the Specials came into the sales are rebuilt with a different kit than yours

 

[nj1639]

I would focus on the charging Check First .. It is simple to do .. Se what the charging voltage is when machine warm

Yep.
One of the best and overlooked improvements to these machines is a mounted volt meter.
Nothing much better than seeing your voltage when the key is turned on, watching the charging recovery after start up and then seeing it level off as you ride. Checks off a few boxes of electrical health and function and let's you know if a gremlin hops on to your ride.

 

[SolidGhost]

Looking at your XS pics you do seem lucky enough to have those early version 78 vacuum peacocks.
Those early ones are the best and most trustworthy!
If you order a rebuild kit be careful. The next mass produced version as the Specials came into the sales are rebuilt with a different kit than yours

Awesome thanks for the tip. And ha. Autocorrect got me. At least the thread’s staying active! Also, interesting. Everyone on here is telling me I have a 78 but it’s titled as a 77. I checked the numbers via the thread here and got “77/78.”

 

[SolidGhost]

Yep.
One of the best and overlooked improvements to these machines is a mounted volt meter.
Nothing much better than seeing your voltage when the key is turned on, watching the charging recovery after start up and then seeing it level off as you ride. Checks off a few boxes of electrical health and function and let's you know if a gremlin hops on to your ride.

I’ll have to add that to the next round of upgrades. Makes perfect sense.

 

[40north]

When MTBE was added to the petro it disintegrated the vacuum cock and acted as you described.
The stuff fubared lotsa other peoples' machine too. fyi> https://archive.epa.gov/mtbe/web/html/gas.html

Those finks made me a very irritated fella! Pushed that xitch for miles.