1982 Seca 400 DOHC loss of power

[OntarioSeca]

Hi guys,

I'm having some issues with my bike. Bought it 8 years ago with 2300km on it. Ran fine after I bought it and changed the oil that had been sitting for over 20 yrs. Had very smooth acceleration and top speed was impressive, around 140 km/hr.

I took it off the road about four years ago and only take it out for about one or rides per year. So basically its been sitting.

Problem: Only starts with choke fully on. Revs up high on start up and have to play with choke to get the idle down from 4-5k to around 1200rpm.

Now when I release the clutch I get very little power and the throttle response just isn't there. The gas is fresh, plugs are fine, fresh oil and filter.

Any suggestions. Petcock, vacuum leak or just dirty carbs?

I've been searching on here all week and for the past hour and just don't know where I should start? Though I should ask you guys!

Thanks!

 

[JaredK]

Welcome to the forum!

The choke (or enricher on these bikes) will make it run higher, around 3k. The point is to get the engine warm up to operating temperatures. Let it run for a minute or two to get it warmed up, and it should idle back down around 1200 when you have the enricher off.

Slow throttle response is usually a sign of a lean mixture (i.e. it's not getting enough fuel, or it's getting too much air). Check for air leaks. Start the engine, and then get some starter fluid and spray it around the carb boots, vacuum port on the right side carb boot that's supposed to be plugged (manifold side), and the vacuum line from the petcock. If the idle changes when you spray, you've got an air leak.

Do you have a fuel filter on it? You should be able to see if gas is flowing freely. If you didn't have a filter, something might have moved down from the gas tank and is plugging your carbs. You'd need to clean them out.

Try that out and see if it shows anything.

And post a pic when you get a chance!

 

[OntarioSeca]

Thanks for the reply.
The bike will not fire unless the choke is on full but once it turns over the rpms fly up to 5-6k and won't drop unless I play with the choke. Even after warming up I still need the choke on a bit to keep it running.

I haven't had a chance to spray around for leaks yet. From what I have read on this forum it sounds like that is the culprit. I did pull the plugs and they were quite dark, almost black. They aren't very old plugs either. Maybe 1500km on them.

No fuel filter on the bike.

I will get a pic as soon as possible up loaded.

thanks

 

[OntarioSeca]

I apologize for the late response.

I warmed the bike up and was actually ab;e to get it to idle with out the choke on at just under 1000rpm.

So i sprayed wd40 (all i had readily available) around all of the the intake boots and around the petcock hoses. No change in idle at all.

I removed the air filter and found that the foam gasket had disintegrated, so it doesn't have a really tight seal.

I bike still is lacking power. When I rev it the response is very slow to increase to 6000rpm. And it doesn't drop back down as quick as it has in the past.

Photos to come

 

[OntarioSeca]

Pictures

 

[Lou Ranger]

If I had to guess, I would say that some of that air filter gasket has been sucked into the carbs.
My second guess (if you are using regular gas or premium with ethanol) would be with such infrequent use, the ethanol has been separating and plugging your carbs.

Once you get them clean, you can't beat the low cost of prevention with a $3 filter, and very easy to install - http://www.xs400.com/forum/showthread.php?t=7574

 

[willem]

coming from a previous seca owner with similar problems: clean those carbs!

and +1 on the filter

 

[OntarioSeca]

I'm definitely going to add an inline fuel filter.

As far cleaning carbs I've only had experience cleaning a honda xr 100 carb once. Anyone have a link to a cleaning how to? I have located a decent video for the procedure on the seca but I'm not feeling really confident about getting everything apart and back together without any issues?

Thanks in adavnce!

 

[JaredK]

Just did this yesterday. This should be helpful:

Removing the carbs from a DOHC bike:
http://xs400.com/forum/showpost.php?p=134577&postcount=3

Disassemble the carbs (pretty much the same as the SOHC):
http://www.xs400.com/forum/showthread.php?t=12330

Cleaning carbs (boil them for best results. Also, I'd remove the butterfly valves because there are rubber washers/gaskets in there):
http://www.xs400.com/forum/showthread.php?t=11541

 

[OntarioSeca]

Thanks!

Looks like I have some work to do