running rough...

[redroadster68]

After months of sitting idle, ye olde roadster is back on the road today. I stored it with a full tank to reduce tank condensation, added stabiliser to the fuel. didn't touch the dual solexes at all. car ran great when I parked it.
Car starts great, idles a bit rough, light popping from tail pipe. idles at 900. Under light acceleration it sputters and bogs down. heavy acceleration it bogs. . . BUT, after 15 to 20minutes of driving around, everything smooths out. acceleration is strong and smooth from idle to over 5000rpm.
What I've already done: changed the fuel filter. ran the tank to half full of the winter gas and added 94 octane to top of tank and added 1 bottle of methyl hydrate to combat any water that maybe in tank. sprayed carb cleaner into carbs.
thought it might be water in tank because intial driving the water would be at bottom of tank then the more I drove it would get mixed and car would run smoother....thoughts?
I don't think its jets because it ran great last year and it presently runs great after it gets over its hiccups. I don't think its plug or plugs because...again it does eventually run great.
the only thing that's happened ...sure its not related but ill mention it.. the clock has always ran and ran all winter. in the last 2 days ive had to replace the fuse that runs clock twice...what else does that fuse effect?
thanks all
1968 Datsun 2000 solex

[Gregs672000]

Fuel seems likely... jets etc don't suddenly change and not work right . Sometimes the accelerator system in the Mikuni can gum up and that can cause some stumbling on acceleration. Check your plugs and see what they're like if it continues.

[Toptech360]

I just went through this with my pressure washer lol. Definitely sounds like gas. Next time your car goes into hibernation put non ethanol gas in if it's available near you.

[redroadster68]

pressure washer hahaha....
if its the gas, how come it eventually runs smooth after a bit of driving?

[Gregs672000]

You said it boggs under acceleration... if it were not getting fuel, it would bark through the carbs most likely, so it again sounds like bad fuel to me. If it doesn't clear, remove your air filter etc so you can see down the carb throats with a mirror and light, then (engine off) pump the throttle by hand and make sure each throat is squinting fuel out the accelerator jet (you'll see it).

[redroadster68]

ill blow through this tank of gas to as low as possible then fill .

[jrusso07]

I have had good results with Marvel Mystery oil in the gas, especially with non-ethenol fuel. It keeps carbs clean as well as valves. I also run it in the engine oil for a 100 miles before an oil change.

[redroadster]

How free are the carb slides / pistons ?
Does it hrlp if you choke it a bit
How easy is it to suck fuel up with a vacuum pump , the S bend prob.
Valves set right?
Ign timing ?

[cktrap]

Quote "didn't touch the dual solexes

[redroadster68]

so this morning I started the beast, let it idle for 15 min then drove it. yesterday I filled the top half of tanks and added stp water remover. once on the road it bogged and sputtered. after 10 min of driving it finally smoothed out. drove it for a good hr of city and highway driving and it was awesome. pulled through the revs from multiple stop signs and red lights....god I love driving this thing. wound it out to 5700 rpm a few times....purred. I just parked it. I will take it out this evening...letting it sit and cool off 4 hrs
on a diff topic, when idling, what does your oil pressure read? I will continue to burn through this tank of gas over the next few days. ill get it to as low as possible before filling again .

[redroadster68]

shot in the dark here... could it be a seized up thermostat? car runs crappy until reaches temp. worked fine in fall but sitting over winter it seized? any thoughts?

[redroadster68]

I let it sit for 5hrs cooled off in garage. took it out for a late evening rip. ran great. no hesitation through the revs to 5000. maybe I ran through enough of the "bad gas". I have just over half tank so I will run it down some more tomorrow, day off. ill add another stp water remover when I fill it up next.
its awesome driving at night with the top down....

[spyder]

Before I park mine for long term I turn off the fuel pump and run the carbs out of gas so it dosen't sit in them. I also fill the tank with non-corn gas. All I can get around here is 87 octane although it requires me to pull timing, it causes me less driveability problems. The corn-gas boils in the carbs and causes all kinds of mixture problems at slow speeds, like leaving a light. It will act flooded and I have to floor it to clear out the vapor. For the longest time I thought there was something wrong with the carbs but since there is a gas station now that sells non-corn gas I know the gas is the problem.

Now to speculate on the OP problem. Perhaps you have a partially gummed up jet causing this problem. A car needs a richer mixture when cold so perhaps yours is just a bit too lean until it warms up. If you have gummed up pilot jets, they are not re moveable and would be harder to clean.

[redroadster68]

Thanks everyone for your input... you guys are great and knowledge appreciated.
Last night I ran the tank down to just under a 1/4. I filled it up with 94 octane again and also added my 2nd bottle off stp water remover.
Had an awesome evening drive with the top down and the car ran great. This afternoon I took it out again for a 45 min jaunt out in the country.
So I’m very happy to report that it looks like it was less than perfect gas. Thanks again everyone for your input. I guess 6 months sitting, gas degradation was worse than I thought it would be. I read lots before winterizing it... maybe grain gas is the culprit. I’d thought that today’s modern fuels would have so much freakin stabilizers, preservatives, and god knows what to make fuel last at a high level for more than 6 months.
Next year maybe I’ll find pure gasoline... somewhere... or bourbon. A heck my baby deserves champagne ... geez then it would really bubble and fart. All the best guys ... until the next issue ...

[greydog]

I use Stabil in the mower, 300zx and roadsters in the winter.
Seems to work pretty well.
Dan