Re-tuning a 73-77 Titan?

skids · Post by **skids** » Fri May 01, 2009 11:05 am

I've always wanted to ask about this.

In 1973 Suzuki factory de-tuned the T500K with changes to the inlet port and the carburettors robbing almost 3 hp and reducing the fuel economy.

I have two GT500's, how hard is it to re-tune the engine? The 3 hp would be nice, but I really would like to improve the mpg.

H2RICK · Post by **H2RICK** » Fri May 01, 2009 9:28 pm

Hmmmm.....well, big bore air cooled strokers are NOT the most efficient engines ever created...so it's never going to get 50 MPG....unless you ride down a lotta hills....and don't ever have to ride back up 'em.
What altitude do you ride at mostly ??? The closer to sea level you are, the better your efficiency will be.
What grade of fuel do you run ?? High-test will give you somewhat better mileage and, yes, the economics DO work in favour of high-test.
Oh....avoid the ethanol-extended crap fuels if at all possible. These bikes were NOT built with alcohol fuels in mind.
What gearing are you running ?? The stock 500 gearing is biased towards mileage rather than performance so it's best to stick with the stock sprockets.
How's your chain ?? A worn out chain can cut your fuel mileage BIG time.
Just a few idle thoughts.....

skids · Post by **skids** » Sat May 02, 2009 5:06 am

Don't be silly Rick, I trailer it back up the hills.
I'm in Halifax NS, I can spit and hit the ocean, I'm running premium from PetroCan, stock sprockets, the chain is good, I avoid idling, and haven't had a thought in years

What I was wondering is how hard is it to improve the intakes and the carburetor to reverse the Suzuki's 1973 de-tuning for day to day riding. Most of the porting specs I've seen are for adding extra race performance from pre-73 engines.

rngdng · Post by **rngdng** » Sat May 02, 2009 8:33 am

I'll tell what NOT to try. Don't put the short intakes onto your GT500 cylinders without completely rejetting it!! With the short intakes, there isn't enough velocity to pull enough fuel through the main jet, so it'll run very lean, and hole the pistons.

Lane

skids · Post by **skids** » Sun May 03, 2009 7:53 am

That's a good bit of information

rngdng · Post by **rngdng** » Sun May 03, 2009 7:59 pm

skids wrote:That's a good bit of information

Yeah, Dofin found out the hard way after I sold him my GT500. I was quite embarrassed.

Lane

skids · Post by **skids** » Mon May 04, 2009 6:33 am

I looked up the VM32SC carburetor jetting differences between the J, and the K to GT's.

T500J
Main jet: 150
Needle jet: P-5 (right) P-4 (left)
Needle: 5FP8 3rd position from top of clip
Pilot screw turns out 1.25

T500K to GT500B
Main jet: 97.5
Needle jet: P-4
Needle: 5FP17 3rd position from top of clip
Pilot screw turns out 1.5

I also found this difference in the float heights:

Model T500J to M
Float height: 27.3mm

Model GT500A/B
Float height: 25.8mm

skids · Post by **skids** » Mon May 04, 2009 6:36 am

That means I have set the pilot jet to te wrong spot, 1.25 turns instead of 1.5.

I think I'm going to double check my float heights as well.

rngdng · Post by **rngdng** » Mon May 04, 2009 10:22 am

Just keep a close eye on the plugs. That's your best indication of what's really happening. If I had checked mine, I would have caught it in time.

Lane

Craig380 · Post by **Craig380** » Tue May 05, 2009 2:04 am

Wow, 150 mains to 97.5 is a BIG drop

I see what Lane means about completely rejetting ...

bikegeezer · Post by **bikegeezer** » Tue May 26, 2009 8:28 pm

skids wrote:That means I have set the pilot jet to te wrong spot, 1.25 turns instead of 1.5.

I think I'm going to double check my float heights as well.

I'm thinking the air jets and other carb settings may be different as well. Have you considered installing a set of pre-'73 cylinders and carbs? I'd think that would be a slam dunk.

Stu

skids · Post by **skids** » Wed May 27, 2009 5:06 pm

I'll probably do that when I find a really nice set of early barrels, it just feels like a shame since my GT barrels are barely worn in, heck they're still std bore.