73 Eldorado sputtering & surging under load

[Odradek]

Hi,
I've a 1973 Eldorado that is currently driving me crazy.
Had it laid up for the winter, and didn't put any additive in the fuel like I usually do.
That said, on my first ride out it was fine, for about 10 miles, and then it started running a bit rough.

This started a period of about 2 months where I've spent most weekends trying to get it running right, and I'm still failing.
I've installed new fuel filters, new fuel lines, had the carbs off and disassembled twice, and have cleaned the point and set th ignition timing a few times.

I was having a problem with serious backfiring, but either the last carb clean or the last timing adjustment has sorted that.
Now the bike is starting and idling fine. It will rev up like normal, but, as soon as you start to ride, the engine under load starts spluttering and surging, as if it's about to stall.

Can anyone offer a few pointers as to what I should be looking at next ?

I've even resorted to asking Google AI or help.
It says the gas cap vent maybe be blocked or the distributor advance may be seized.

[Antietam Classic Cycle]

Have you removed the petcocks from the tank and cleaned the filter screens or at least verified that fuel flows well? Possibly a failing condenser or even ignition coil. What's the history of the bike though? Has the engine or even just the top-ends been rebuilt recently? It might be best to start from the "beginning" - retorque the head nuts, and adjust the valves. Fresh plugs. How old are the plug wires and caps?

[Odradek]

Thanks.
Yes, I guess the petcocks are next to check.
Stein-Dinse, where I usually buy parts are out of stock for the next 8 weeks they say.

Heads were retorqued late last year and the bike has hardly any miles since then.
I've no info on the bike's service history before I got it, 3 years ago, apart from discovering it was restored by Mark Etheridge at Moto Guzzi Classics sometime in the 90's.
I do have a spare coil sitting on a shelf in the garage. Honestly can't remember if I changed the ping wires, though it did get a new distributor cap about 2 years ago.
It does seem to regularly need new spark plugs though, and I've never figured that one out.


EDIT :  I've ordered a new condenser and some petcock gaskets. Coming from Germany so they could take a week to arrive.

[Antietam Classic Cycle]

What country are you located in? That helps with parts recommendations.

[Odradek]

I'm in England.
There are one or two Guzzi parts specialists here, but I've found for older bikes they often tend not to have things in stock.
Have had best results ordering from Stein-Dinse in Germany, who carry a huge inventory.

[Tkelly]

I had a bike that did something like that until I rode it with the choke on,then it ran fine,I don’t remember what the fix was.

[TN Mark]

Did you empty the tank of the old fuel and fill part way with known, fresh gas? If not, why not?

What's the condition of the inside of the tank? Rusty or fairly clean. If the current petcocks and/or the filters are clogged, you've found the result of a rusty/dirty gas tank.

[Odradek]

Have drained and refilled the tank twice since this issue started.

[Vagrant]

I had a bike that did something like that until I rode it with the choke on,then it ran fine,I don’t remember what the fix was.

That screams  plugged low speed jets.

[guzzisteve]

You might want to check your timing advance, make sure the screw under felt pad hasn't got stuck or tightened up. It's on the center of distributor rotating shaft. Under the cap & rotor. Just an idea.

[Cam3512]

Here’s a little ditty.  May or may not help.  Years ago I’m heading back from a rally on my Eldo.  Same symptoms .  Drove be nuts.  Stopped and changed plugs a few times.  Got home and noticed the small screw that held one of the distributor clips had disappeared.  My cap was bouncing around at speed, but settled into place when I stopped. Never knew it.  Discovered it in the garage.  AND the screw was still sitting on top of the engine block.  Can’t make this shit up!

[Aldo]

This may not apply for your case, but here it is anyway:

I was having an issue with my '73 Eldorado that would only manifest itself when the engine was at operational temp. The bike would sputter, pop, and want to stall at idle, but only when hot.  I checked valves, cleaned carbs, checked the points, timing, and swopped condenser, plug wires, dist cap and rotor, spark plugs and caps,  and even the coil.  Nothing.  The Eldo would start fine when cold and settle in a nice idle, but when it got hot, same thing...sputter etc. 

Then I noticed the issue... I am running later tonti heads with exhuast studs vice screwed collar, and when trying to start the Eldo while hot, I noticed one of the headers vibrating quite a bit.  When cold, the exhaust gasket would seal properly, but once it heated up, basically it created a large gap where gasses could escape.  One side was very loose, the other less so. Additonally, the flange on one of the headers was cracked...so i rewelded it, replaced the gaskets on both sides and sealed them up. Problem gone. 

Again, this may not apply in your case, but make sure those exhaust gaskets are sealing properly and the headers are good and tight.

[Cam3512]

Then there was another time my Eldo was coughing and spitting.  Finally found one of the wires wasn’t full seated in the distributer cap.  It became all gunked up with carbon. Cleaned it off, seated it deep, and done.   

[Odradek]

Thanks for all the advice.
I have now replaced the condenser, and installed new points for good measure.
Just took it out for a quick ride around the village and it seems to be back to running as normal.
Hopefully I get some time tomorrow to take it on a longer ride to make sure.

[Antietam Classic Cycle]

Thanks for all the advice.
I have now replaced the condenser, and installed new points for good measure.
Just took it out for a quick ride around the village and it seems to be back to running as normal.
Hopefully I get some time tomorrow to take it on a longer ride to make sure.

Expect the new points to close up a bit as the "rub block" breaks in. A little Bosch Distributor Grease on the lobe helps to keep to maintain the point gap longer.

[guzziart]

Thanks for all the advice.
I have now replaced the condenser, and installed new points for good measure.

On a somewhat related note, in Spring of '19 the house a/c stopped working.  According to one of my usual info sources (youtube), I came to the conclusion that the motor Capacitor could be the problem and could be tested with a voltmeter having a cap test function.  Well, I've got 4 vom's and none had a cap test function.  So, I ran over to the local Home Depot and bought a Klein Tool VOM w/Capacitor test function for $70, ran home and tested the a/c capacitor with my new toy and concluded the capacitor was bad.  The local HVAC supply house sold me a new Cap for $9 and our a/c then worked.  Maybe I shoulda just threw parts at the a/c unit and saved $70.  Anyway, I now check the capacitors (aka condenser) on all my ignition points equipped stuff since during routine maintenance...becau se I have a VOM with a cap test function and because I want to get my moneys worth out of it. So, that 's my condenser story.    Glad to hear Odradek's Eldo is back to full functionality!