Seca 750 NOT GETTING FUEL

Slow Ride
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Seca 750 NOT GETTING FUEL

Unread post by Slow Ride » Sun Jul 31, 2016 7:28 pm

Well guys, I cleaned the carbs on my 82 Seca 750. I thought I was so smart and that the bike was going to run like a new one. Well last night after trying everything including spraying starting fluid into the air box, I finally got her to start. Now it acts like it is not getting fuel at all, the chokes dont seem to do a thing.
I thought maybe the needle and seats were sticking and no fuel was running into the bowls, so I popped the bowl screws loose and gas runs out of every one. When I cleaned the carbs I made sure all the jets and little holes were clear and open.

Now I am starting to wonder about VACUUM. Is it possible that for some reason the engine isnt producing any sucking power to draw the fuel up into the carbs?
I hope some of you guys can help me out getting to the bottom of this. After the bike has sat for a couple hours and I go to start it it fires and pops a couple times, then nothing, just crank and crank and no fire choked or unchoked, nothing. Then I squirt a load of starting fluid into the air box hole, now it fires right up and will run for about 10 seconds until the starting fluid it gone. So I know that my plugs are good and have ignition. Just need to figure out why the fuel isnt getting to the combustion chamber.

Help! Slow Rider

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Re: Seca 750 NOT GETTING FUEL

Unread post by Gummiente » Sun Jul 31, 2016 7:52 pm

I'm not sure if you know this or not, but a thorough carb cleaning that involves disassembly and removal of jets will require adjustments and synchronisation afterwards. This involves hooking up a flow gauge, aka carb synch tool, to ensure each carb is flowing the exact same amount of air as the rest at any given throttle position. A generic sequence is as follows; Idle mixture screws should all be set at 2.5 to 3 turns out from bottom, jet needles should all be set at the same height, idle speed screws should be adjusted so they just touch the throttle drum and then wound in an extra turn and the throttle cable should be loosened off so that there is about 1/4 turn of slack at the throttle grip. Once these settings are established, the bike is started and the synchronisation is done at idle speed, then the throttle cable is adjusted to remove slack and synchronisation is done again at about 1/4 throttle setting.
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Re: Seca 750 NOT GETTING FUEL

Unread post by Slow Ride » Mon Aug 01, 2016 8:02 am

Sounds like I am off to the Yamaha dealership to spend $400 bucks on a tuneup
Of a $200 dollar bike.

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Re: Seca 750 NOT GETTING FUEL

Unread post by Gummiente » Mon Aug 01, 2016 8:28 am

Slow Ride wrote:Sounds like I am off to the Yamaha dealership to spend $400 bucks on a tuneup
Of a $200 dollar bike.
Sometimes, unfortunately, that is the cost of buying an older bike. When I worked at a motorcycle dealer we had many people drop by with old bikes they had bought on the cheap but couldn't get to run properly. Sometimes they faced hefty bills far in excess of the original purchase price, sometimes they got lucky with a bill of only a few hundred dollars. Before you head to the Yamaha dealer, I suggest you visit a few of the local independent shops, if there are any in your area. Some brand name dealers will actually refuse to work on bikes more than 10 years old, while independent shops are more willing to help you out. They usually have less overhead costs and charge less than the dealer would for the same job.
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Re: Seca 750 NOT GETTING FUEL

Unread post by Slow Ride » Mon Aug 01, 2016 2:32 pm

Thanks for the advice. I called my friend Steve who owns Steve's Machining. He used to work on Yamahas and he knew exactly what I have. He says the 750 4 that I have came from the factory with poor valves and poorly seating valves. He says the reason it wont start or run is it needs valves ground or replaced. He said, bring it over he will fix it. I asked how much, he said not over $400. I have had him do work before and his quotes are accurate.

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Re: Seca 750 NOT GETTING FUEL

Unread post by GS_in_CO » Mon Aug 01, 2016 8:51 pm

Have you ever seen the bike work? Or is this a bike rescue?
Without a compression test it's too soon to know if it needs valve work.
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Re: Seca 750 NOT GETTING FUEL

Unread post by Slow Ride » Mon Aug 01, 2016 9:57 pm

Yeah I have put 8K miles on it over the past 5 yrs. Ran perfect has been going down hill in performance each year.

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Re: Seca 750 NOT GETTING FUEL

Unread post by GS_in_CO » Tue Aug 02, 2016 7:37 am

Then valves are a possibility. But your friend Steve still owes you a compression test for proof.

The t-shooting forum here gets a lot of questions without background or context thus my question above.
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Re: Seca 750 NOT GETTING FUEL

Unread post by Slow Ride » Tue Aug 02, 2016 10:35 am

Ron You are right, I will remind him to do a compression test. Maybe it needs rings, but he will get it running.

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Re: Seca 750 NOT GETTING FUEL

Unread post by Gummiente » Tue Aug 02, 2016 11:05 am

If he's a competent mechanic, a compression test prior to any work performed is a given.
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